Hand 1) The only hand that calls a bet on a flop that is unconnected and unflushed is the one that beats you. Other than that, you SHOULD have bet harder...but I don't think he would have folded his overpair.

Hand 2) Probably a good fold, but I'd reraise here for info, a minbet is pretty fish. I'd suspect something like AJ (for TPTK) or JQ (for TP + straight draw)

Hand 3) Your check shows you're scared of the 3rd spade, I'd bet here too regardless of my hand to try to take the pot. Fire a bet here, if you get reraised, you fold, if he calls...you get to see and lose the smallest amount possible, if he folds, you win.

Hand 4) I call 3-6bb raises all day with any PP, knowing that people will pay me off greatly at these limits when I finally hit. You should be making the same move. I'd much rather limp, but (I play 6max btw) I'm not folding my PP to just a standard raise