Have a questions regarding pot odds and hopeing for some help.

$1-2Limit game:

1.In the middle position with QTd, two limpers, you call, one raise to the left, call, small blind folds and big blind calls. It comes around and everyone calls. So there's 11.5 bets for $11.50. The flop comes Ac 8d 6d. Betting goes bet, fold, you raise, call, fold, call. You have a flush draw, with 31.5 bets for $31.50 ( if I missed something or am not saying in correctly please let me know what I missed..I'm concerned that I'm not getting the pot odds correct) The turn betting goes first person bets....If I'm on the right track the correct play is to either call or raise because the "pot odds" are 2-31.5 or 1-15.5...one bet to win 15.5... and with 9 outs.. the remaing diamonds... my pot odds are greater than the break even odds of 4.1-1 I'm not concerned with implied odds just yet so.....haven't quite figured that out yet...

2. If the turn card come up a blank regardless of what the betting is, is the correct play to fold because you didn't make the flush on the turn or continue to the river. It seems that because the pot odds would remain the same if everyone checked or became bigger that the thing to do would be to stay in the hand because of the pot odds and the number of cards that can still help....

3. Is there a "magic number" for pot odds? seems like pot odds of 1-4 or better depending on the #of outs is what one is looking for...

A long post and I hope I didn't get to confusing and looking forward to the replies

Thanks