Calluses on your hand are unavoidable. So are bruises on your legs. I bruise easily too, but I don't care if I have bruises.
Just wear whatever you normally wear to work out. Lots of girls just wear a tank top or t-shirt and shorts.
I don't eat beforehand or after. When I first started, I used to drink a protein shake after crossfit, but I stopped doing that in favor of IF. It doesn't bother me, but everyone's different.