How often do the shuttles from hertz to LAX run? Or.. how much time should I allot from dropping car off to getting to airport to allow enough time to go through security? Extra 30 mins?

During the day, plan on 8 minutes to wait for the bus to arrive and load, then another 5 minutes to get to LAX. If you aren't in the first terminal though, you should add another 5-10 minutes; traffic can be congested slowing each stop.

I gave myself an extra 30min and cut it close ... I'd say 45min just because check through at lax can take forever.

Depends on time of day, usually pretty quick,

I got on the bus instantly and it left. They may wait for more people but there were 3 buses waiting to take people to the airport.