Miami Airport experienced "significant water damage" in the storm. It will be closed on Monday the 11th, and they'll determine tomorrow whether they're able to resume flights on the 12th or whether further repairs are necessary. Each airline will decide when to operate once the airport reopens.
Miami Beach was evacuated and will not allow people back in until Tuesday the 12th at noon (and then, only residents with ID) and some areas are flooded today. 75% of Miami-Dade County has no electricity right now, and the county is under a curfew. It is likely that your hotel doesn't know whether they can operate or whether they have power and won't know until after the roads reopen and staff can reach the hotel.
There's likely to be a lot more clarity by Wednesday, after they've started to clear the roads, people have had a chance to get back into Miami Beach, electrical crews have begun repairs, and the extent of the damage is surveyed. The city does "foresee" being open to visitors by Thursday, but you'll want to keep an eye on their communications and the Miami Herald newspaper for updates. That said, to me, Friday seems quite early to visit Miami Beach.
Personally, I'd change my trip to start someplace else in the US besides Florida on the 15th, keep an eye on the news, and go enjoy Miami starting on the 26th, assuming that things are sufficiently open then to have a good time.