Hey Dragonracing, at Lou's Speedway we have run an enduro race sort of like the series you're starting, except it was a single event not a series.
For the most part our teams were a more experienced driver with a newer driver, or someone who already has a usgt car and someone who wants to try the class out.
We ran 2hrs. Locked fdr at 4.5 to keep things a little more even.
There was a sort of "assembly" start where they started with the battery out, body off, and wheels off. After that, pit stops were up to the teams. Run till lipo cut off or don't. Swap drivers when you want but both drivers have to have the same amount of stick time.
It was a big hit! Guys had so much fun that there is a second one coming up. Mandatory lights have been added to the rules for this one and length has been increased to 2.4hrs. The lights to the building will be shut off for some or all of this race. Although it won't be very dark. The track has 6 or 7 windows about 4' x 4' along the length of it about 10-12' high. It provides a lot of light. Enough that racing in the dark shouldn't be an actual problem, just an interesting twist.
Goodluck with your series!