How to know which is suit to get for racing and training?

So I'm not to sure what size suit to get for both swim practice and meets. I'm not exactly sure either how to tell if the suit is to tight or not. I was told once if you can get it on without struggling it isn't tight enough, but I'm not sure if they were serious or not. I'm a 30/31 waist normally, and a guy..since that will make a difference I'm sure. Oh also, I know technical suits are illegal for meets but I might be able to get one for cheap. The only thing I'm curious of is if there is a difference between the male and female versions of the kneesuits are(cover the chest to knees)? I've checked measurements on myself and it matches with what the measurements of the suit is I can get for cheap. Does it matter what the "sex" of the suit is if its just for swim practice?