You could also look into Ubiquity network equipment. They make a variety of networking products and access points. Overall, you don't really have a -huge- area to cover, and some of the access points they sell have ranges far in excess of what you're looking to cover. The tricky point is your router and bandwidth. While most basic residential routers can handle a dozen different devices, upping that by 10 creates some strain on them. Thus, having a commercial grade router comes in handy to take care of routing and such as it also generally has better control over traffic shaping, QoS and the like.
Assuming that you can run the wiring and hardware, I would say 6 wifi access points (three on each floor spaced out) hardwired to a...