there are some excellent information sources on cisco.com & other links on performing a site survey. I recommend the 802.11 wireless fundamentals book from ciscopress as a good start.
The coverage will be dictated by several factors, such as obstacles, rf interference, access to data & power, etc.
The # of APs needed for a survey will vary with the size of the area that is to be covered. 2 APs hardly makes a mesh. You will not get a true idea of how the mesh behaves, fails over, etc with just 2 APs