Eating the superworms would be better than not eating anything at all. If you can see if they have any that are notfull grown. As long as your temperatures are fine he shouldn't have too much of an issue with digesting them. But I wouldn't let him gorge on them. Try to put a carrot or potato in with the superworms too for an hour or two before you offer them. This will help add some nutrients.
I would be cautious about moving him to a bigger tank. It could trigger relocation stress and he doesn't need any more stress right now.
Does he usually lay up there on that hammock to bask? Seems pretty close to the lamp. Is it hard for him to get up there?
What is the temperature on his hammock? Specifically the surface temp, not the temp of the surrounding air.
-Brandon