Hi Nick and welcome to the forum - I do not know the Trend jig, but I looked at the manual on line, and on pages 36, 37, 38 it shows setup, routing the tails, and routing the pins.
The tails are cut with the dovetail cutter and the straight slots, and the pins are cut with the straight cutter and the tapered slots. This conforms to other units of this sort, notably the Leigh which I use. Your unit seems to work in a similar fashion to the Leigh, except that the Leigh has variable spacing. If you can find instructions for the Leigh on line, it might well clarify some of your other queries regarding set-up.
I hope this helps you with at least one part of the process, but perhaps someone else can weigh in on your other queries. I have no idea what the circular discs could be.