I'm doing Sweeney now. We have a two level set with upper galleries on SR and SL, and a bridge that rolls US/DS between them. We have a bunch of flies (the chair flies in), and a a bunch of rolling pieces that come and go (pie shop table, oven, grinder, Pirelli stage). We also have a "landing platform" that comes and goes, and connects to the main chute on the bridge for the chair trick. Our open set has made a few things tricky, like getting Pirelli out of the trunk after he's killed.
Is your theatre renting a chair rig, or building something? Be sure to build in time on set to get your victims used to that ride, as it can be scary at first. We are also doing a TON of blood, with a trick knife that spurts, and a blood bib for the shaving victims that is cheesecloth lined underneath in vinyl to protect their costumes. The blood just drips down it. But it does get everywhere.
We have a pretty large ensemble (15), but thankfully we do not have a lot of costume changes (instead they're shifting our moving pieces during most scene changes). They have a basic costume, then they change for the ball for Poor Thing, but that's it. We're doing Fogg's Asylum as shadow play, and then our City on Fire sequence is dark and red and you don't pay attention to the fact they're wearing the same stuff they've been wearing throughout.
I second the call for lots of music rehearsal in your schedule. Not only is it sung through, but this is very tough music. I will also suggest that if your Mrs. Lovett, Johanna, or soprano ensemble members are wearing corsets in the show, to see if you can rehearse with them. We ran into some trouble with the blocking/high notes being much more difficult once they got into corset.