Hi Sean
A lot of questions there so I'll do my best to answer what I can.
You may be able to use a single AP mounted centrally in the building depending on where you are (and hence the power regulations associated to your country), the level of throughput you need, and the actual size of the building. Here in the UK we are limited to 802.11b (currently) and 50mW radios, but even with 2.2dBi antennaes the AP has a coverage radius of about 40m at 11Mbps - so, depending on whether you are nearer the 200ft or the 300ft mark will define whether you need another AP a bigger antennae (bigger antennae, bigger range and/or different coverage pattern). You need to perfrom a site-survey in the area to be certain. Also you need to consider the number of clients that will be using the WLAN - being as it is a shared media you get performance equivalent to a 10 meg hub scenario so you would be looking at a maximum of 20 users with 'normal' traffic patterns (email, browsing etc). More users will mean more APs - and you can co-locate up to 3 in one area, but you must use different channels (for 3 APs the only channels that will do this are 1,6 and 11). The Cisco kit will 'load-balance' in this scenario, with the client associating to the 'best' AP - and you are correct about them needing the same SSID in order for the clients to roam between them.
Also - you need to ensure that the environent you are surveying is as close as possible to how it will be in operation - i.e. you say it is empty at the moment, but if you fill it full of cardboard or trees or dogfood (whatever) that will impact on the coverage from the APs because of multipath, signal absorbtion etc.
Cisco have a large range of Wireless equipment and sundries, and your one-stop-shop url for all things Cisco and Wirelessy is www.cisco.com/go/aironet.
You may also want to have a look at the Wireless LAN association website at www.wlana.org.
Hope that helps - Best of luck!
Kev
