Have been to Saturdays with PIARC.
They run 4 groups.
Open Wheel
Race Cars (v8 super cars, GT cars etc ec)
Experienced Drivers / Fast Cars
Inexperienced Drivers / Slow Cars
For you, I would select Race.
As for who turns up....well anything.
I have seen, Lambo GT, Porsche Cup cars, V8 Supercars etc etc.
You also get the guys out for a paddle around the track, but they will be grouped in the slow group.
The Fast Group is really anything faster than 2mins. Race is anything faster than a 50 from the time they were doing.
These days are a line up, once the track reaches max density for the session that is it. You wait. Though I have never been in the fast group with more than 10 or so other drivers on the track.
You can get CAMS on the day, though only if you are a PIARC member?
Did you get RaceChrono up and running? As there is no timing on Saturday with PIARC.