Most of use doing a lot with WiFi and m0n0wall use dedicated APs and standard Ethernet on the m0n0wall. The WiFi performance within FreeBSD simply can not compare to a real commercial grade AP. (also, you can't hook up several of them to light up a large area...)
So, your support will be limited as most of us would rather spend a few dollars, over spending a lot of time getting a cheap and low powered USB device working.
It is a bit of work to save $87!
http://www.amazon.com/Business-class-High-power-Wireless-n-300MBPS-Access/dp/B005SSQHTM/ref=sr_1_1And that is for a very good, high powered, N capable AP.