Just wanted to address this.
Relaxed yes, that is very important but it’s the kind of relaxed that only a professional athlete would know, ready to spring at the speed of light. There’s a velocity of movement that’s more important than torque eventually, yet initially it feels like torque is more important as your work your way up the skill tree, there will come a point where you develop the strength and precision and torque control becomes secondary to a velocity dynamic.
Picking hard? There is no constant picking intensity eventually, it’s what you feel on the passage for dynamics and will come naturally. There is only controlling attack and amp response. Initially you will try to go for even play with compressed dynamics, but as you get better you will find the dynamics develop purely from feel.
Holding the pick. Your grip will evolve, but for most efficiency you will find the pick fully extended with the thumb bending thing critical. There is no curl on the index finger, and the contact patch with the thumb too is as far as you can take it, away from the bone joint. This gives you reduced motion eventually, high efficiency, but this make take some evolutions to achieve, watch Roma Lee’s right hand to understand what I’m trying to explain. Surprisingly this became a thing for me when I realised it forces a kind of angle that increases the percussive attack tremendously, especially on upstrokes. This works on a stratocaster, but not on an LP type, I find due to the guitar my hand rests differently and the pick rides closer to the thumb joint, I’ve just started playing an LP type guitar and I find what works for YJM on the strat does not translate to the LP. Also the taut nature of the shorter scale string ( I’m using the same YJM gauge, but tuned to std.) I find the bounce back feedback from the string different even though I don’t feel the string tension any different on my fretting hand. The bridge being higher away from the body makes a difference on how I anchor, I seem to anchor much less, with with the strat I’m almost always anchored.
Using the same picks as YJM, us mortals need to buy the purple 1.5 Dunlop picks… initially I’d scratch the pick with the point of a knife to create a burl checked pattern on both sides for grip, eventually that became just one side, and then I soon realised this wasn’t necessary as the flat surface would be quite sticky naturally. This is like riding a bike on a high gear with almost no throttle, you feel like you’re going to lose control but you don’t. Pick tension is different for everybody, some hold it too tight for my tastes and that translates low dynamics and a stiffer sound, that’s fine if that’s what your are going for, but for that floaty wailing with moments of sheer terror, the dynamics I think are in a more relaxed grip. Starting out you will not know what is optimal, but just make sure your using a plexi type amp, driven by a real DOD YJM 308 or his red fender pedal, else you will not achieve the right environment to develop the touch. The plexi could be a plugin like spark for example, they have a great emulation, I have a real plexi and that thing I find comes closest with one of the real YJM hardware analog pedals.
Also some how I don’t think of YJM as a shredder in the traditional sense, to me he’s more like a time travelling 17th century violin player. Listen to lots of classical violin and celine dion, it’s all phrasing, else it’s just “shred” 
Hope that was helpful and not pointless.
edit: just want to say this is my experience with all this… your mileage may vary. Don’t like writing all this down in a public forum when you don’t know how it will be taken. Thanks.
Another thing that I do that further hampers me is that I think that my “rig” behaves as if it has compression, and that saps dynamic range as well.