If you are looking for the theoretical Maximum number of users per AP (most experts would recommend 15 to 20 Max);
Here is a cisco doc that relates to this question;
Q. How many clients can associate to the AP?
A. The AP has the physical capacity to handle 2048 MAC addresses. However, because the AP is a shared medium and acts as a wireless hub, the performance of each user decreases as the number of users increases on an individual AP. Ideally, not more than 24 clients should associate with the AP because the throughput of the AP is reduced with each client that associates to the AP.
First of all do your environment really needs roaming? as most of the users are static in any environment. Well for mobility to work in your environment you have to install the Mobility controller to handle all the access points and the users movement among them.
Regarding the number of APs, if the density of APs is high as in a school, is it good practise to deploy them one per classroom, using the 5GHz channels to provide more channels to avoid radio interference. The APs would be LWAPP and controlled by a WLC. Otherwise please suggest how to distribute APs in this environment.
In some areas of our Campus we install the AP's in a 1:2 config. One AP above the wall that joins two classrooms. The choice to use 5GHz "A" radios sounds like a good plan. The Channel settings can be nicely handled by the WLC using RRM (Radio Resource Management) This doc has an excellent overview of RRM;