From a Software perspective, 3200 series can certainly cater upto 32 APs, which ever AP it is. But the challenge lies in design. Let us have a look at Firewall and Encryption Throughput of the 3000 series.
Firewall through put 3600 controller is 4 Gbps and AES-CCMP throughput is also 4 Gbps. If customer requirement can be met with this, then you can go with 3600. If not you need to go with 7000 series.
For this you need to work with your customer on what is the expected peak traffic generated by an 11ac client in average and document it.
As an extra tip we have started supporting Uplink aggregation through LACP on AP 225/ 224s. So they can have an uplink of upto 2Gbps. This is different from actual traffic generated by the client associated to the AP.