did you bleed the system?
any leaks?
do you get hot air?
does running heat lower engine temps?
are the fans decent? not ebay crap that have 1/4th the CFM
Use a stock temp thermostat
bleed the air out of the system
car not starting is a common issue in the Celicas, the 12V line gets heat soaked and does not send a strong enough signal to start the car. Solution is to install a rely, wrap the wire in insulation, or just keep it cranked for 30 seconds, if it doesnt star, pop the hood and let it cool off for 5 minutes.