Two main issues; security and bandwidth.
Wireless network security needs to be addressed from the outset, you really want to back up your WLAN with something like Cisco Secure ACS to make sure it's as watertight as you can make it.
As for bandwidth, AP's are like hubs, shared medium so all clients share the available bandwidth. Partial solution is to pack AP's closer so fewer clients per AP but this needs careful surveying and planning.
Other considerations are AP management, look at some of Cisco's newer solutions for centralised AP management/configuration. If you have lots of AP's you will need something like that to make the system manageable.
