Flywheel resurfacing min thickness

I'll be installing a new clutch in the next couple of weeks and I'm looking to have the flywheel resurfaced.
The questions are:
How do I know if it can be resurfaced BEFORE I take it down to NAPA?
What is the min thickness for a 122 tooth flywheel?
I'm pretty sure I can mic the flywheel from underneath with the lower plate removed if that would do any good.