Good questions. Actually, the width and depth of the alignment slot is set by parameters in CabWriter. The default width is 5/32″ and 1/2″ depth, but they can be changed. The width of a biscuit is 5/32″, so you’re right, 3/16″ would be too wide. I normally use #10 biscuits and I use a 1/2″ deep groove in the carcass sides and slightly over 1/4″ deep into the face frame. If you go much deeper into the FF, you won’t get a good bite with the pocket screws because they’ll end up in the groove.
As for the Quirk, I typically use a 45º chamfer bit in a trim router, and yes, you have to set it for a very shallow cut.
I hope that answers your questions, let me know if you need any other information.