First question. I would assume the answer is yes, but I'd like to see what other players think.

Can you rest with zero strain tokens just for the purpose of removing dmg?

I've seen other players state that if they have no strain, they will spend a surge to gain health.

Is that correct?

The rule book only states that resting will allow you to gain life. Spending the surge isn't classified as "resting"

rules say that everytime you recover strain and you don't have strain tokens to recover, then you recover health instead.

so, you can rest with 0 strain tokens and heal damage tokens only. and the rule of 1 surge recover 1 strain when you attack, also heals damage if you have no strain.

the same for Fenn and his "Lone Wolf" ability