Pot Odds Calculation - Help! - Need trips or two pair

[NotStudying]

So I'm trying to calculate the pot odds for the following situation: I have two low cards in the hole and I'm against one caller (suppose I was BB or on an ill-advised bluff). I suspect they have a higher pocket pair, and on the flop I hit one pair, which still can't beat his pocket pair on its own. I either need to make trips, or get two pair.

I can calculate the chances of hitting trips or two pair easily enough: I have 5 outs, and 100% - (42/47 x 42/47) = 20% that I'll hit one of my savior cards. (Please correct my math if I'm wrong.)

I have three questions from this starting point:

(1) How do I account for the risk that he'll hit HIS third card?

(2) Are the risks of hitting quads, full house, straight, flush, etc. significant enough to warrant taking that into consideration from this point?

(3) Is this really an appropriate pot odds calculation in the first place, since you may have to bet/call/raise after the turn as well?

Thanks...