1 there is a new weapon, but not pickax although that would've been a good idea I think.
2 you can collect gold ore, yes.
3 you do get sent there during certain bad ends, but not as like a playable segment
4 unfortunately no, as nice as that might feel haha. Completely overthrowing the slave trade is probably beyond the scope of the game, but you do get to kickstart the process in the next release
5 no, and probably won't be a thing I think.