A dance floor, apart from the guest area, can take a significant portion of floor space. Calculate at least 250 sq. ft. for a dance floor, considering more for a larger guestlist/
Some events call for a separate lounge/reception area, apart from the dining space. The space should be at least as large as the dining area if everyone were expected to stay for an extended period of time. If it is meant to be a through-space, it can be smaller.
For events requiring stages, careful attention should be paid to the type of performance. A standard quartet or band would probably not need more than the basics, but a "big band" would need, apart from a reinforced stage, a large amount of floor space to accommodate all members, as well as space for a speaker.