Hi Twilight Spiral,
A troupe is for people who already know how to belly dance. I hope you asked about getting lessons, not joining the troupe!
The costumes are great, and of course you can buy a few to wear at home or when you go out. I know some local men who make good $ in a dance show at the local club, some with exotic costumes. Learning to dance well will help you to look better in a belly dance costume, and put on a better show (whether public or private).
Men in belly dance class (straight, gay, fond-of-crossdressing, whatever!) usually wear t-shirts, shorts (of moderate length) or yoga/track pants with proper underwear, and a scarf tied to obscure their "package". I have also been in classes with a male who wears a skirt, but I generally feel that's not the best way to start out. Most of the women will be wearing long pants, so it's better to do the same.
If it is very important to you to wear full costume while learning dance, you may need to work at home with a video, or arrange private lessons. Just like ballet and modern dance, belly dance has "class dress" and "performance dress". If you want something belly-dancey for a group class, look into Melodia pants. They are very dramatic, and flattering to both sexes. But please do not start in class with a cropped top. I think it would just be too distracting for the beginner ladies (or maybe that's just me
)! Save crop tops for later. You can chop your practice tee a
little shorter if it obscures your hips.