To vent or not is personal and also depends on the helmet itself. We use open face helmets for both stock car and SCCA/NASA events simply because that is what I've used for longer than most have been alive around here. Is it safer than a closed face-not necessarily. If you are driving either an open wheel or open top car-then by all means use a full face-much better protection from things flying over the top of the car like rubber bits.
Both Bell and Simpson have models that are made to help cool your head. However, the use of a headsock/balaclava is a good idea when it is really hot. You can also do one of several very expensive things that the NASCAR types are now using for head cooling.

The most important thing we can tell you is to buy an SA2000 helmet and go have a good time. Autocross-it is off more than it is on. Road race events and HPDE you won't have it on for more than 45 minutes at a time usually. Enduros are a different deal. Just be absolutely certain that it fits properly-very snug in all directions. My Bell MAG4 is very tight and the earpieces can be a pain-but I am not uncomfortable overall.

Did I mention my new wife is very finicky about how I look

Happy Holidays