1.) I've called way too many of these and lose pretty much all of them.

2.) Raise-call the flop, there's only one hand you worry about.

3.) Probably a set of threes. This is never a bluff.

4.) Bet the turn. This is a draw heavy board (two flush draws now!) Do you think he would slowplay a set on a drawy board...doesn't seem too likely.

5.) Check-call. There's a few two pair combinations you beat, and against an unknown with no reads you can't put them solely on the nuts.