You will have 2 Virtual controllers in there...
the limits as you said for AP 93 is 16
For all other models is unlimited....
But if you have let say 17 105 and 1 AP 93 the limit is reduced to 16...
IF you got the budget you can always get a controller a 3200 :) you will get more features and better handling for higher traffic plus less tagging, as in the IAP you will need to tag the vlans you usinf for your SSID for each AP...
Anyways think it like a future project maybe? you can convert those IAP 93 in normal APS anytime you want when you have a controller.
Anyways does this answer your quetion?
Cheers
Carlos