Considering we currently share about 17 kids between football and band, and we are already sharing a practice facility (at different times of course), it would be exactly the same as it is now which is no problem at all.
Secondly, yes I will want to use it often. Will I have every rehearsal in there, no of course not! Next year, I have no idea how my full band will fit inside the band hall including pit and drum line. Being able to have music rehearsals in an open area gives us a lot more breathing room than our band hall which will be wall to wall next year. Being able to split our groups and have multiple marching/playing rehearsals at the same time without sound bleeding, especially each one having a met.