A single access point won't be awesome for 50 people on a 20Mbps pipe.
Wifi is a shared medium and it degrades quickly as you add hosts. Two people streaming Pandora over wifi will make git checkouts a pain for other people.
Also keep in mind that every smart phone and ipad will also want to access that same wifi.
(so that's maybe 100 end points?)
I prefer to hard wire desktops/laptops (especially for developers) in a startup environment. Switched gigabit ethernet is a lot cheaper to deploy than wifi, and the performance is easily two orders of magnitude better...
If you must have Wifi and since you seem to be sold on Cisco, maybe take the 2106 series wireless controllers? I've used their bigger brothers with good success.
They help by optimizing signal strength of your cisco APs for the environment.
Choosing which access points to pair with the controller is trickier.
There's usually a price premium for N, so I'd consider G-only (1130 model) if your budget is tight.