One overcard to a pair is about 30% (give or take couple % if suited), same as being dominated. Lots of combinations of hands, but most outs are to three cards (about 2% an out five times). Try plugging hands into a poker calculator. Cardschat has one, requires a download I think. There's really no calculating to do preflop (other than pot odds
on an allin) there are only several types of 2 card matchups, just learn the odds of them. Pair over pair 80/20, dominated hands 70/30, live cards Ax v Kx 60/40, pair v overs 50/50 and a few others slightly different.