Re: Many locations, less APs and clients with same SSIDs
What Leo mentioned is good to reduce the signal from bleeding out too far, but I would also maybe reduce the power level of both the 2.4ghz and teh 5ghz. Without really knowing how much you need to to cover is the question.
Now as far as how you would deploy this, I would configure all the AP's in h-reap/felxconnect if possible. This way you can drop the traffic off locally and define the 3 vlans on the network locally at the site and not back at the location the WLC is located. You will need to trunk the access point ports and allow the managment vlan along with the three vlans for the SSID's. Take a look at the design guid for h-reap/flexconnect. This way you don't need to confiugre 300 interfaces.