From the manual it reads ," When running the generators in parallel , the total amount of power available between all receptacles is 3000 watts " So i would say 3000 is the cap.
This cable will not work to jump a car. If you have a generator that has an auto start system via battery it should have a plug to use jumper cables that could jump a car. If you generator does not have a auto start system you can power a charger from 110 v outlet on the generator to charge a battery.
12 AWG is what is stamped on the outer shielding.