Storm Assault reminds me of Hammer the Gap in Pathfinder - pretty brutal / powerful if you get lucky in landing the consecutive hits, but random enough so that it doesn't seem blatantly OP.
I would perhaps tweak it however - so you only set up the chain hits if the hit rolls are over a certain number or something... I'm sure others will have a better ideas regarding this though.
The avalanche ability seems cool to me - especially used before a whirlwind attack, that seems like it could be effective.
The firmness feats seem like a canny investment to get the best out though, especially when we already have the armour specialisation feats for medium / heavy armours that give characters DR 3/.
I like that it's a consideration of light armour wearers though - though I don't know to what extent I could picture someone being able to get the 'best' out of studded leather in the same way as they could from heavy armour.
Maybe if it was 2/ and less encumberance, higher dex bonus from wearing the armour?
50% negative energy resistance seems like a lot for the Chaotic Influence feat, though I like the idea of feats around the shadow weave - I'd say either drop it down a bit to 25/30% or offset it with a penalty - vulnerabilty to positive energy or skills or something?
I like the other trait feats you mention as they factor in a penalty for a benefit.
I also like the shadow weave magic feat idea too - can't really say whether I think it's balanced or not as I don't play casters, but I like it conceptually. Will be cool to have similar stuff in future potentially linked with wild magic.