What I suggest doing is pick one dance grouping and do the dances you feel comfortable in. But do two levels, if you can afford it.
For my second competition, I did smooth and rhythm, and 2 levels in each. Newcomer and Int. Bronze (no pre-bronze was offered.)
For a ladies dress, what I wore for the first one was horrible. But for the second one, I went to a store that sold formals, found one on the clearance rack that had a full skirt. And had it shortened, added some long matching gloves, and DANCE PANTS! Cost about $120. Still wear it when I've gained a few too many pounds for my competition gown.

Make sure that you can raise your arms above your head. For Smooth and standard, spread your legs out sideways as far as you can, bend over and stick your arm through between your knees. That'll let you know if it's full enough (watch out for the slip, why they stick straight slips under full skirts??). For rhythm and latin, just about anything off the rack will do (try to avoid black, you won't stick out), just make sure it's sexy and won't ride up on you. If it has a little flounce in the skirt, even better. Dress rehersals are a good thing.
But if you can get to a competition and watch beforehand, especially with if you shadow a competing dancer, that is the best prep of all.
And Lastly, the one thing that nobody tells you about until it happens, if you feel depressed or moody afterwards (extreme PMS??), that's okay. It's just the low that happens after the adrenline high.

Been there, done that, I've heard it called "Performer's orgasm."