calculating odds in drawing hands with 10 player tourny tables

So if you are trying to caculate pot odds of hitting a flush on the river and say you are calling to get 6 to 1 on your money...since you technically have 9 outs you have basically 1/5th chance of hitting your hand so it is a fair call. But if you are in a 10 person table 18 cards are out of the deck, either folded or alive, so even taking a conservative estimate you are probably down 3 of your 9 outs. So is it "right" to take into account the fact that the odds of actually having 9 alive outs is almost nil and maybe guessing you have 6 outs so a 15% chance of hitting, in which case you no longer have pot odds? Obviously if you are playing with 4-5 other ppl this doesn't matter that much.

Also some random questions.

If you limp in with say a suited A8 with pretty good position (or lets say you are on button) if you hit the A on the flop how do you bet the flop if everybody checks. The way i see it since you limped in the odds are no one has JJ+ or AK/AQ. But there is a reasonable chance some1 limped in with A9 or something. I normally end up betting the turn with something about 1/2 the pot just to try and get an idea of where i am at. It's fine if they fold or if they reraise (so i fold) but if they call i don't really know where the hell i am in the hand. They could be slow playing a set or something if it is heads up and they are confident they have best hand that probably won't be beaten. And say you limp in with A8 or something on one of the blinds and hit an A on the flop. Do you check/fold and hope that you hit an 8 on the turn or something? Would be nice if some1 could share how they tend to play hands like this. I'm just not very good at playing A with a low kicker.

We can't ever know what cards our opponents hold, and thus we calculate our odds strictly on the basis of probability in terms of known vs unknown cards. If you're factoring the number of cards of said suit in your opponents' hands, then you also have to factor in the rest of the deck as well.

If we flop a flush draw, we know that we have two of said suit in our hand, and two are on the flop. We can see 5 of the 52 cards, so that leaves 47 remaining cards. 13 of said suit minus 4 of said suit (2 in hand, 2 on board) leaves 9 remaining in the unknown part of the deck. 47/9 = 5.22, and so your odds are 4.22:1 from flop to turn.

A flush draw is always 4.22:1 to hit from flop-turn, 4.11:1 from turn-river, and 2:1 from flop-river.

Your second question is completely situational and can't be answered without more information. In general in those situations we'd like to keep the pot relatively small.