I love you Chris.

Here are some suggestions for managing the events, coming from an experienced hand:
Driver cap at 36 - 12 cars per group, assigned groups upon tech inspection, to be altered later depending on driver skill level. At 45 mins per group and a grenerous 45 seconds per run you will get at least 5 runs per session, x 3 sessions = 15 runs per person, making it a better run/dollar ratio than an autocross.

Tech inspection - have a tech tent close to the pits for people to roll into once they've unloaded and before they are set to run. Not performing a tech ninspection can really be setting yourself up for delays later on.

No dead time - having more than one person at the starting gate will ensure that any talking to's or radi communuication don't interfere with the regular rhythm of sending people.

Cool-down zone - 2 cones set up as a gate along the return path to shut people down from getting wild and invincible will let you send the next driver all that much sooner.