For wall mounted APs, we are currently using Oberon right-angle mounting brackets (HERE).  This is to ensure the APs are positioned correctly. 

The way the current deployment is described, 2800 will fit the bill.  You won't see any benefits using 3800 & 4800.  I don't see any benefits of using the 1800 either.  

If your switches are capable of providing up to 30w then you're fine to use 2800.  You won't need mGIG nor will you need to use the 2nd port.