I tried everything on, pinned up half the hem of the underskirt, then put the overskirt on, pinned up half the hem of that, and pinned it in place where I want bustle tapes to be. Naturally, putting on the overskirt made the underskirt too long again, so I re-pinned that hem. Then I put the bodice on, and realized that while the neckline and hem seemed to work, the darts were way off. They a) went about 1-1.5" over the bust point, and b) probably because of that, took out too much fabric through the bust, so the bust was way too small. The unfortunate thing is that I have a feeling there may be some scarring in the velvet where the stitching was. I really hope it's not too bad. By the time I did all that, it was already about 10:30 (aka, past my bedtime), so refitting the bust darts will have to wait.
But at the very least, tonight I can pin the whole hem of both skirts in place, so that I can start hand-sewing that at rehearsal tomorrow night. I was originally going to do a facing instead of a folded over hem, but I have a fair amount of length to fold over, so I think I may just go that route. Also, it's easier.