re: salsa clubs i have not a clue. Check out time out rome. It has the best info on that kind of thing.
Clubs would either be out in the boonies (noise) or in testaccio. If in the outer burbs, you are going to have to cab it.
Museums -- Romans love museums. I like the little known museums in Rome book which you can get through amazon. I like the galleria spada and palazzo altemps, there is a nice little gallery off the cloisters of santa maria della pace. The brazilian embassy may have something nice on too. Good way to see some pretty neat buildings.
There are some great gardens, but the weather that time of year is sort of iffy. Could be horribly rainy, could be bright and sunny and cold.
As for Florence -- easy day trip on the eurostar. Can buy tickets from machines in the station and avoid the lines and rail europe.
lala