8 rummies sounds good. Super tight school & great display! 8 (maybe a few more) rummies, a couple nice bushynose, and a pair of GBRs will make a sweet set-up. I'm kind of jealous, LOL.
Throw in some otocinclus(4-5), a small school of pygmy cories(6) and some Amanos(5-10) and your set-up will be a fairly complete and functional ecosystem.