Re: AGC in FSK receiver
I could probably think up a reason to have a front end AGC, but it would be a real stretch! Maybe if you can only do minimal bandpass filtering up front and do not want stray intermods coming into band from strong interferers.
In an event, except for those unique situations, a simple limiter at the end is all that is needed.
If you have the option, you want to do the final IF bandpass filtering as close to the limiter as possible, for "click noise" reasons.