ArubaOS 8.x is not designed to work in a large-scale network without an MM. If you had an MM, you would be able to:
- Cluster your controllers for automatic redundancy
- Automatically distribute licenses to the controllers that need it.
If you loaded all of your licenses on a single controller without an MM, you should be able to point the server without the licenses to the server with the licenses with the license server-ip command: https://www.arubanetworks.com/techdocs/ArubaOS_83_Web_Help/Web_Help_Index.htm#ArubaFrameStyles/1CommandList/license.htm
To answer your question, in practice it is recommended to only run controllers at 80% capacity. The capacity of your 7240 controllers is 2048*2 = 4096. 80% of 4096 = 3276, which means you are very close to capacity for those two controllers and you have no room for redundancy You would need a third controller to support failover. You probably should manually decide what access points should be on what controller with lms-ip in each server group. You do not have any capacity to do any type of HA.
Everything I said above is with the limited knowledge of your network that you provided. Since you have 3200 access points, please consult your Aruba Sales Engineer or Aruba Reseller for specific and proper advice about what steps to take to make your network more manageable. Not having an MM or an additional controller will force you to manually manage things that ArubaOS 8.x was designed to manage automatically.