The venue for an event should be chosen based on what sort of an event it is and any associated themes. The venue could be anything you like, whether it's a loft, a flat, a hall, or a room.
Guests at a buffet eat standing up, picking up as much food and drink for themselves as they like. It may be better to have a venue without too much furniture for this, so that people can move around freely as they mingle and eat their fill.