It depends, if you want to do any firewall, user roles etc then a PEF-NG license is a good start too. Also the RF Protect license is good for spectrum monitor and WIPS stuff. You need to make sure that each license level is the same as the controller will support the minimum license count.
So for example
2x AP Capacity
2x PEFNG
2x RFP
The licenses are permanent and do not expire. The licenses are applied to the controller and not the AP.
You could always request an eval from HPE to trial features first, these are valid for a maximum of 90 days.