Never hire a band without listening to the recommendations of past clients. If the band sounds great but you can't get any decent recommendations from people who've hired them before, there's got to be a good reason. Drop them from consideration, and move on to the next option.
Musicians usually work pretty hard, so be sure to give them the breaks they need. In the course of a standard four-hour reception or similar event, most contracts require that the band has 3-4 short breaks, and one longer meal break of at least 20 minutes' duration.