Hand 1: Raise for a free showdown is probably fine, calling down is OK too but I don't like that with the flush draw out there. If this was your last hand at the table you could fold this but I'm concerned about metagame aspects of folding to a donk bet when an ace hits.

Hand 2: You got a backdoor flush draw and two overs: Check raise the flop and see where you're at. If he 3-bets the flop you call and fold comfortably on the turn unless an ace or king hits. If he calls your check raise bet the turn and probably bet the river unless a J, T or 6 hits. Calling down here is bad.

Hand 3: Bet/fold the turn. I'm a little worried with UTG's aggression but you don't want to be calling a random river bet. Get the money in while you might be ahead.

Hand 4: Limping here with QTo sucks. You can be easily dominated, you don't have good connectors and you're not suited. Maybe other people do this but I think it's a lousy play. If you wouldn't limp with KTo, don't do it with QTo (QJ and JTo are marginal limps at best here.) That said, bet this flop. You'll often get a free card and if you're c/r'ed on the flop you're only paying one more small bet to see if your straight comes on the turn, and your implied odds are probably better at that point. Also, if you bet this flop and get raised, it doesn't put you in a bad situation when your T comes on the turn and you agonize about your decision as you're doing here.