Building a Wireless Network for an Apartment Complex?

itwerx asks: "I've been asked to design a wireless infrastructure for an apartment complex. Tenants will pay an 'access deposit' and a monthly surcharge to get a PCMCIA/PCI/USB network card along with free installation and, of course, wireless Internet access. The buildings are arranged such that 2 WAP's per building should cover all the tenants (one WAP per side, far enough away to get line-of-sight through the windows). I do have a few concerns, however. All help is appreciated and when we're done we'll put up a HOWTO!"

"My concerns are the following:

• Interference between WAP's (there's several buildings) - there are enough channels if we go 802.11a but cost is a concern.
• Management of 'hitchhikers' - we're planning on manual assignment via DHCP/MAC address for tenants with others having all their HTTP requests get directed to an info page. Anybody done something different?
• Interference from WAP's and other devices that may be owned by tenants! Should we just avoid the default channel and hope for the best?!?

What other things might I need to worry about?"