When wearing panties, do you have to tuck your male genitalia out of the way? Is it uncomfortable to do that all day?

I've had my testicles surgically removed (makes tucking a lot easier!) and I've been out dressed before, but thus far I'm still wearing briefs (no one can see what underwear I'm wearing anyway, since I'm wearing pants). I'm thinking of checking out panties so I'd like to find out more.

Oh, and how do you know what size panties to buy?