There are several outfits on CC (besides Sally) that are quite capable of helping you to plan your party. We at the Auxillou Beach Suites do party planning as well, as well as does Maria at Vega Inn and Gardens.
That said, there are no local bands on the island nor flower shops. Your best bet would be to have someone arrange those things for you, as they would need to liaise with numerous locals to get enough fresh cut flowers and to bring musical talent in from the mainland.
Live bands can be quite expensive to bring to CC, because you have to pay for hotel, transportation of the instruments, etc.
How big is your party in terms of attendees?
I think a restaurant would only block an evening off for you if the business you will be brining in will be more than if they stay open.
Thanks and cheers,