Although some of the best ballrooms are to be found in nice hotels, you may discover that they don't allow any loud music, due to the ballroom's proximity to the hotel residents. Often, however, they will allow acoustic music, especially if it is subdued.
Often (but not always), you won't be allowed to bring your own alcohol into a rented ballroom. Be sure to check with your ballroom's management about local restrictions. If you'd like a cash bar, it's a good idea to notify the caterer well in advance so they can arrange any necessary licenses.