One question though, does the Walk in Shadows (Scoundrel skill) work with Guerilla as well?
I don't believe so, but I'm not sure. Walk in Shadows makes you
invisible, not stealthed. Though it does kind of seem like there should be some synergy there.
2) Maybe you should retain your backstab bonus on the same foe for a single round (ie. you can't re-stealth but you can take a single guy down probably all the way).
This makes sense to me. First attack from stealth 'marks' the target, and then for the rest of that turn you get bonus damage against them.