I haven't really given it a thought to be honest. Either 2 or 3 car incidents?
Yeah, they'd definitely be cautions. Though I wasn't sure what to do for single car incidents. If the car is blocking the track, that could possibly be a caution. If there's more than one single car incident (different parts of the track at the same time), this may also depend on whether one or more cars is blocking the track.
I also read through the OP again, and there's a couple of things that need changing:
Race start at Indy is 3 wide @ 80mph, restarts are 2 wide @ 100mph. The start and restart speed at Daytona is 100mph.
Indy cautions: 4 caution laps in total. On the first lap everyone gathers behind the safety car. At the start of the second caution lap, the wavearound is given to any eligible cars. At the end of the second caution lap the pits are open. Cars catch back up to the safety car near/at the end of the third caution lap. Cars go double file on the back straight on the 4th caution lap, ready to restart. Leader takes the inside line as it is an oval. Race restarts at the beginning of the pit wall.
Daytona cautions: As above, but only 3 caution laps due to the pitane being shorter. Drivers should be able to catch up to the safety car in time to go double file on the back straight of the 3rd caution lap. Race restarts at the start/finish line, just like every other course except for Indy Speedway.
Leader gets a choice of the inside or outside for road course starts/restarts, and everyone else lines up double file accordingly.
Possibly add a note to Daytona Road that you are allowed to cut through the empty pit boxes on the second half of the pitlane.
80mph may be too fast/unsafe for road course pace/caution laps, perhaps 70mph instead.
Bump-drafting isn't allowed on any track.
I wish there was a way to race the AI with online physics, as I want to do some practice races with other cars on track.
I'm also expecting a lot of incidents in the first couple of road course races, if our 3 car races at Laguna Seca are anything to go by.