1. In a 3-player game, players still choose their titles, going clockwise around the table... starting with the player who was chosen as 'First Player'. The main difference with the 3-player game is that the same titles can't be picked two turns in a row. For example... lets say 3 titles are chosen from the middle circle on the first turn of the game. On the second turn, those 3 titles can not be picked. Players choose from the remaining 3 titles (the two on the outside and the remaining one in the middle), starting with the 'First Player' once again. On the 3rd turn, all 6 titles are fair game and that cycle starts over.
2A. INCOME - Cards that give you a +X bonus to gold do not give you that bonus the first turn they come into play. This is because gold has already been collected before you get to Marshall. On the flip side, cards that reduce the cost of certain cards, can be used right away, because all you have to do is kneel those (typically).
2B. INFLUENCE. Influence just needs to be kneeled, so you can use it on the same turn it came into play, as long as it isn't already kneeled.
3. I have a good idea, but I'm not 100% sure so I'll let someone else take that one.