About the different types of Fortinet Wireless Controllers

FortiWLC - this is the ex Meru Platform (Fortinet Acquisition). Supports Single Channel (aka Virtual Cell). It is a dedicated Wireless Controller platform. Tailored to high end, high density, corporate, and voice over deployments.

Integrated - this is AP management via a Wireless Controller that is built into a Fortigate Firewall. Dos not support single channel.

Cloud - AP's are managed via a cloud service. Does not support single channel.

No, not exactly. There are dedicated AP's for each platforms however some AP's are 'universal' AP's which can be flashed with different firmware depending on the management systems. These are typically branded as FAP-Uxxx where the 'U' refers to Universal.

All AP's can be cloud managed.

2.Do I need to change the firmware of the FortiAP depending on the controller I will use?

See above. If you have the Universal AP then possibly yes, but typically this process is automatically done depending on the controller type that the AP discovers. For dedicated AP's (Integrated or FortiWLC) based, this is not an issue. I would not be concerned about this. The only time you'd need to change the firmware is if you'd changed management platforms after deployment and typically the TAC would assist you with this anyway.

3.  If I am managing my FortiAPs through FortiCloud and my subscription expires, will the FortiAPs stop functioning?

I don't believe they will stop functioning, but you will not be able to modify their configuration without a valid support contract.

4. Do the FortiAPs recognize layer 7 applications when managed by three controllers above?

Yes, Application inspection (monitoring, logging, blocking etc..) is built into both the FortiWLC and Fortigate (Integrated) products. 

Further reading: https://www.fortinet.com/products/secure-wifi/wirelessmanagement.html

Hope this helps. Let me know if you have any other questions.

Bets Regards,

Mark