Time to buy professional equipment. Find your local Cisco sales office and ask them what they recommend both for the equipment - given your requirements - and the company to buy it from. At work here we have a wireless infrastructure supporting 100's of laptops. So it's certainly possible.
http://www.cisco.com/en/US/products/hw/wireless/products_category_buyers_guide.html to start with yourself.
I'm working on the wireless internet for an apartment complex. What wireless router(s) would you recommend that could handle a high amount of traffic (40+ users with a lot of streaming and downloading), with wide enough range to cover the entire building (approximately 18,000 sq ft)? The current system is a patchwork of different routers that has been thrown together over time as demands have grown and unfortunately it has not scaled well and is not well prepared to handle the level of traffic that is currently being placed on it. Any ideas or suggestions on how we could improve this problem would be greatly appreciated, thanks.