Simon,
from watching when my car was sprayed, there was no hardener in the 2K PPG paint i used, but they still allowed 15 -20 mins flash time between coats (in a booth) so i doubt you will need to get right into the clear straight away.
dont forget to Strain/filter the paint. and clean the gun between coats to make sure it doesnt fould up and ruin the job.
as for respirators, not sure, but you might wanna get a disposable overalls to stop the paint getting in your skin (its carconegenic sp?)
airborne contaminates mostly come from the painter - so the overalls will help reduce this, vaccuum the area your painting in after the car is in there and the plastic walls (you should use) are sealed once vacuumed you might wanna prepsol the car to clean anything that was stirred up.
No pro info there, just my ideas and observations.
Chris