Some things with my normal turning:
-I only turn new/unsized brass, as this best fits turning mandrels, full length.
-I turn down neck FL and onto shoulders a small bit(my opportunity to mitigate donuts).
-I do not trim necks first/for turning, or use turning stops. I can easily eyeball ~1/16" onto shoulders which is plenty enough. I trim to correct length only after fireforming.
-I hold the turner body in my hand(floating) while the case is held and spun by a 'case lathe'.
-I use Mobil1 for turning lube, and cool the turner mandrel/cutter with a swish & brush in a heavy small bowl of alcohol resting in a larger pan of ice water.
-After turning I polish the neck a bit with 000 steel wool while it's still on the lathe. This is so I can confirm neck thickness to near .0001".
As far as setting, I'm pretty old school trial & error with a feeler gauge and a couple culled cases. Newer turners provide standard incremental adjustments(I use Sinclair's NT-4000), which is nice but no faster really.
When things are abnormal for turning (up/down sizing, or re-forming neck involved) the trial & error takes a little more effort as I still turn the brass while new/unsized.
It's not an exact science, many ways to skin the cat. Luckily, it takes a lot of effort to screw it up