1) Do you need to learn all the class methods of breathing to benefit from
the heath & martial aspects of Stv?

Yes and No.

The sequence of stances and the breath technique taught at the rll level are very effective for martial and health purposes (the breath technique is actually the 'most advanced' in the system and is basically the same as that of the Knge, I will explain more in a moment) but each of the class methods is used for specialised purposes.

In very general terms, the Karl method is designed for health promotion & the correction of minor problems (more serious problems are generally treated with one or more of the healing techniques e.g. spine manipulation to correct mal-allignment etc.). This generally means that the Karl stances and Galdr (the vocalised breathing techniques or incantations) are a bit of a must for anyone with an existing health problem (e.g. asthma) and for anyone who has heath issues as their main reason for practising Stav
(whether for personal 'health insurance' or to teach as a healing system to others).

In addition, the Karl galdr is perhaps the simplest of the Galdr methods to learn, and thus as well as being very useful for health promotion (which is relevant to just about everybody) it also makes a useful preparatory training for those intending to learn the Herse or Jarl Galdrar.

The Herse galdr is basically a method designed for the "professional warrior" and teaches a (fairly extreme) form of breathing which was designed for use under battle-field conditions i.e. not personal one-to-one combat such as in a duel, but in situations where one may face multiple foes, perhaps over an extended period, and where one may be forced to fight at a pace that is not of ones own dictation. I really need to stress this point a bit; while the Herse breath is incredibly useful martially, it is really only necessary in extreme conditions. In a "normal" fight against one, or even a few, opponents, a Stv practitioner will normally seek to
control the speed of combat and make it suit their owns purposes e.g. waiting in a "guard" position, forcing an opponent to make a very careful and calculated attack and basically setting the foe up. Generally a Stav exponent will dictate the speed of the combat, usually forcing an attacker to slow down (to try to safeguard themselves while attacking) and so on.

Under these conditions, any of the breathing methods work well (I'll discuss this briefly later). However, in a battle-field situation, one might have faced a wall of enemies three deep or more and could realistically expect to have to both attack and defend more or less simultaneously, and as soon as one enemy was dealt with, one would be on to the next. Naturally, running out of breath due to either simple exhaustion or hyper-ventilation was a real possibility, as was having the breath knocked out of one by a chance blow. The Herse galdr is designed to counter-act these possibilities by allowing continuos deep breathing under extreme physical stress, and the instant re-inflation of the lungs. For a professional warrior, these capabilities were necessary for survival but
they would probably not have been much use to someone who was unlikely to fight under such conditions.

In addition, while I would not say that the Herse galdr method is actually "unhealthy" in any way, it does place the body under extreme stress (a bit like training to run a marathon or something) and to counteract any potential negative effects, the Herse galdr effectively also contains the Karl galdr, wrapped around the extended vowel sequences that are used by the Herse.

In modern life (unless you are in the special forces or something) the Herse galdr is pretty much un-necessary, as even in a warfare situation, the nature of battle has changed. This said, the Herse galdr does create a vast amount of Mott and Megin in a practitioner as well as creating a psychological level of determination that can be hard to oppose in combat.

Some of my students also practice sport-oriented "martial arts" such as Tae Kwon Do, and they have found the Herse galdr to very useful within the contexts of these disciplines, both in basic breath control when fighting over a large number of rounds or bouts, and also in both body conditioning to resist blows and to recover from blows e.g. side-kicks to the solar-plexus, which knock the wind out of the body ; the Herse galdr allows for instant recovery in such situations which can be both very useful and
surprising to an opponent.

Before coming to Stav I trained in other martial styles (mainly Chinese) and Qi Gong systems, and spent a couple of years practising the Heavenly River Monastery system of  "Hard Qi Gong" (my Sifu, Michael Tse, always used the term 'Hard Qi Gong' for this art, although the more commonly known names are "Iron Shirt" or "Golden Bell") and I can see a lot of similarities between the Herse Galdr and Hard Qi Gong, although there are probably more differences than common features.

As with the Karl galdr, and indeed the Herse galdr, the Jarl galdr also has health benefits. Personally I find it the most 'relaxing' of the galdr methods but this should not be taken to mean that it is any less demanding. The Karl galdr basically seems to encourage a harmonious balance between (physical) relaxation and contraction of the muscle groups and respiratory system. The Herse is also balanced in this way, but the practice is more extreme - the relaxation of some muscle groups is instantaneous (e.g. the
stomach muscles - this is used to turn the stomach into a bellows to suck air into the lungs by creating a vacuum) while the  ontraction of the stomach muscles is equally extreme (they are progressively tightened and tightened on each vowel sound, forcing all air out of the lungs; I have myself occasionally developed bruising on the abdominal muscles (when I haven't trained in the Herse galdr for a while) and I think this is due simply to the extremity of the muscle contraction).

The Jarl galdr is a little different again. Here the physical relaxation is fairly notable, there is really very little effort is performing the stances at all. However, there is perhaps a greater level of mental or rather spiritual focusing than with the other Galdrar methods. I don't think that it is being anything other than realistic to say that the correct performance of the Jarl galdr produces an 'altered state of consciousness' which is a little unusual; personally (when I'm getting it right, and we all suffer 'off' days) I find that the most notable effects are an unusual balance of 'dreamlike' quality at the same time as a minute focusing upon detail, coupled with a very dislocated sense of time - I generally prefer to practice the stances outdoors somewhere, and I have on
occasion noticed natural phenomena such as falling leaves while performing the stances. The slightly odd thing is the way in which 'external' time simply seems to 'slow down' while the 'internal' mental processes don't - I've watched a leaf fall from a tree and while I 'know' that it fell at a normal rate, I had enough time to make observations about the leaf and its falling which produced the impression of the fall taking many minutes.

The Jarl galdr produces a very relaxed  state of being which has many health benefits as a side effect, but it can also be very useful martially for reasons that I am sure will be obvious...

So in brief, the Karl method probably produces the best all-round health results and is the most useful for the average 'man in the street'; the Herse is particularly useful for body conditioning and all-out combat, and the Jarl method is most useful for meditation, communion with the gods and spiritual practice.

Despite this, each of the galdr methods have positive effects for use in health and martial practice, and it is really a matter of 'horses for courses' - what does an individual most need? Martially, the Karl breathing works very well with the Karl principle and
techniques, which are predominately (physically) defensive and can be expressed as the 'water' principle of moving to a safe position, controlling and then counter-attacking if need be; the breath in on a movement and breath out on a movement works well with this principle. The Herse breathing works well with the more overtly combative Herse principle and techniques, which can be described as a 'fire' strategy, of beating an attack with a (counter) attack and then making oneself safe, and the Herse
breathing is especially useful in taking out one opponent and then moving directly on to the next without a pause for breath. The Jarl breathing with its associated 'dislocation of time' effect works very well with the Jarl or 'ice' principle, which negates or freezes an attack by placing both attacker and defender in a position where continuing the combat is impossible (although this state cannot last indefinitely). The Knge breath (which is the same as that of the rll) allows a switching between any of the other elements or breath techniques and can be expressed as the 'wind' principle; unpredictable and (when fully utilised) unstoppable. However, as mentioned, it is generally felt that before the 'wind' or 'Knge' principle / breath can be mastered (unless this is simply ones natural state) then each of the other methods must have been mastered; the important point is that martially the Knge principle should arise almost unbidden and spontaneously, and this generally only happens when it has become a subconscious habit.

Likewise, the Knge /trell breath should, eventually, simply become ones natural way of breathing, without any thought involved. It is quite surprising when this happens, but with practice it genuinely does. In my more robust youth, I was very fit and I used to run about six miles a day, spend about 4-5 hours in the weights room of my local gym and then spend a couple of hours in martial arts classes; if I say so myself, I was at the time very fit and I often used to go to the local swimming pool and swim 20 or 30 lengths as a matter of course (although I'm not a very good swimmer, and relied a lot on my fitness - afterwards I always felt that I had had a good workout from the swim). A couple of years ago (having just got back from Skiing in Scotland) I wanted to keep by hand in with winter sports, and went ice skating (I am neither a good skier or skater - England is not blessed with much snow and ice most of the time) and managed after about half an hour of skating in badly fitting boots to take a tumble which dislocated my ankle and tore all the ligaments in the surrounding area (I only just avoided a bad break). Although these days I lead a pretty sedentary life, I've never much like enforced rest, and the fact I could not put any weight on the ankle for several weeks (and thus not even perform the stances unless seated) etc. was a real bother. So I decided to go swimming, as the water would bear my body weight. I should explain that is was a year or two since I had last swum, and I was certainly a lot less fit (in the conventional sense) than I used to be. Nevertheless, and despite the ankle problem, I happily knocked off over 50 lengths and would cheerfully have stayed far longer had the pool not been closing. I found after the swim that I was not hot, sweaty or out of breath, and that while I had obviously used a few muscles that I did not normally use, I was not tired in any way. My only conclusion from this was that, without even noticing, I had been using the Knge / trell breath, which had kept me physically relaxed during the activity and left me without fatigue.

I have generally noticed this effect in many other activities, ranging from martial practice to wood cutting, writing to running - after a while the body responds to any stressful situation not by tensing but by relaxing, not by gulping in air by but by deepening the breath, and all this happens subconsciously. It can be quite odd at times, but I have noticed that this stress-induced relaxation (sounds a bit of a contradiction in terms I know) has become a habit with me, and the more stressful a situation I find myself in, the more relaxed I generally become (useful for myself, but I am sure very annoying for those around me, as often people think that if you aren't joining them in hopping up and down in a state of agitation then you can't be taking a problem seriously). Anyway, suffice it to say that there is nothing whatever inferior about the trell / Knge breath and it really should be practised, not only when performing the stances but in all daily activities such as walking down the street etc.