Re: Playing for draws....
It depends a lot on how many people you have acting after you, what the board is like, and your table. It's also important to remember that you need to be fairly certain that you are not drawing to the second best flush. It's also good to remember that you are paying to see ONE card, not two. People fear the flush draw, and they will certainly do their best to bet you out of the pot when your suit doesn't hit on the turn.
There are other posters here that are better with this question, but I'll give my opinion for the sake of having nothing else better to do right now.
Scenario 1 = First to act - check/call if the odds are right. Last to act - bet the pot.
I check/call because I don't want to give myself the correct odds with my own money should I get check raised.
Scenario 2 = Middle pair + flush draw is great when there's not a lot of action going on. So it's obviously much stronger when you have it in lp and they check to you. If there are two or more people acting after me, I will check/call, or check/raise if I think the bettor is full of it . If I'm last to act, I will bet or raise it, hoping to check the turn should I not improve.
Scenario 3 = With a decent kicker and the right board, I will bet this one all the way down. You'll rep the top pair and no one will put you on the flush.