Dynamite: The rules don't say, but since it is a ranged weapon it seems logical that when you roll to hit with dynamite you only roll a single d6 since dynamite doesn't specify a 'shots' value. Is this correct?
Yes, that is correct. You throw a single piece of dynamite, so that is effectively a ranged attack with one shot.
The dynamite section of the rulebook on page 25 of the rulebook says "Roll once To Hit."
Outpost Bounty: Is this bounty roll applied for the next adventure or the one you just did and, if the former, do the heroes have to return to the outpost to collect the bounty after the adventure?
The bounty is for your next adventure (otherwise you'd have to track all your kills, and that would be a nightmare!), and you do not have to return to the outpost to collect it. Just take your money as you kill each wanted enemy.