I'd direct all those specific questions at OP. I'm merely stating why would it be nice to have them.
I guess they'd be just spawned artificially, or be procedurally generated (like asteroid belt). Creating entire ecosystem for game proved to be not really worth it (Ultima online)
Annoying miners, jumping in front of your ship, appearing mid combat or maybe even some form of attacking players are just extra challenges that can be countered with careful preparation, wise choices and skill. So I count them all as advantages rather than problems. I guess you could also avoid them entirely by staying away from certain high risk high reward areas (i.e. dense core of the belt, old battlefields, abandoned stations).
I'd prefer them to be hunt with normal guns, so hunting ships have some pvp capabilities. That would vastly improve the chance of meeting someone armed in the belt to fight.
Rewards, at least initially, could be just standard materials you can also find in asteroids. Corazium, xhalium, ect.
Are space hunts worth implementation? It's hard to answer that for me, as I'm not game dev, and have no clue how much work it really is to implement it.
So I'm always leaving that argument for devs to decide.
It's also not a suggestion "gib nao!", More like extra flavour for late EA or even post-release.