Questions about poker odds

I always used some simple rules to calculate pot odds and stuff like that, but I decided I wanted to learn how to correctly calculate odds for poker situations.

Stupid question:
Say I want to calculate the probability of someone holding a specific pocket pair preflop:
(4/50) * (3/49) = 0,489% -> 204 : 1 against
That is for one player, and taking my hand into account (I'm not holding the pair). So with 9 players it would be 204/8 = 25,5 : 1 against ? Or is it 204/9 since I have taken my hand into account already?

Another question:
I want to calculate the odds of someone holding 2 suited cards, on a table
of 4 players (including me, I'm not holding the suit).
13/50 * 12/49 = 6,36% 15,72 : 1 (1 player)
6,36% * 3 = 19,08 5,24 : 1 (3 players because I dont hold the suit?)

So I'm in a situation where I'm holding top set, and the only thing that can beat me is a flush (no straight possible, no board pair, but 3 of a suit).
(table with 4 players, as above)
Can I say it is correct to call a bet with my top set, if I get pot odds of 5,24 : 1 or better? Or is the above calculation not correct because I need to take into account the 3 suited cards on the board?

This really kinda confuses me:
Can I just always calculate the probability of someone being dealt a specific hand preflop, or do I need to take into account the cards on the flop?
I know, if I want to calculate the odds of a specific card coming on the turn or the river I have to take the flop cards into account.

I guess I have to take the flop cards into account, because it's additional information that I now have? Is that the correct way to see it? ^^

mh it's late, I'm tired, guess I will look at this again tomorrow :P