#1: Fold. A3 is not a good hand at all at this stage, it'll just get you in trouble.
#2: I bet less on the flop, then probably check/fold the rest of the way.
#3: I suppose I push. A normal sized raise to say t500 is going to commit a large portion of your stack and you can't really fold to a push from someone else. AQo is nice and all, but I don't really want to be playing in a multi-way pot.
#4: You're getting wonderful pot odds to just call. I probably call and try to hit a set.

This is how i'd play these hands. I'm not a super-experienced player, so take this advice with a large grain of salt.