You could hang a 60 watt Ceramic Heat emitter in a dome about 16 inches off the floor of his cage. That will supply instant basking temps from 95F to over 100F. If the center of the hot spot gets too hot at some times during the day, your iguana will just bask a little farther away from it.
I'm assuming that the habitat is large enough to have a distinct hot end plus a distinct cool (75-80F) and shaded zone.
A better answer to how much he should be eating is, "He should have access to enough food to be able to eat as much as he wants." So, putting out enough food for him to wolf down and have some leftovers is a good move. When he eats all of the food, add some more at the next feeding.
You have a great iguana there, Rose. Now I'm starting to consider adopting a rescue.