You can try and cup feed all feeders if he will take them that way. It will let you know how much he is eating and stop the crickets biting and annoying your Cham.
I'd stick with the small crickets, you can start to introduce small dubias (nymphs) aswell. Pretty much anything thats small, Insects shouldn't be any longer than the width of your chams head (eye to eye) Sometimes this doesn't apply when you feed silks/hornworms. They are indeed a better food choice for chams, BUT variety is key.
Also Phoenix worms are a great feeder option, they're high on calcium. Stay away from mealworms. It's hard for chams to digest their hard shells. Waxworms are kinda iffy for me, they can cause food strikes and sometimes fat build up in unwanted places. You can give them as a treat here and there, but i wouldn't recommend them.
Hopefully i helped you out with your question and gave you extra advice, PM me if you have any questions. Maybe i can help you out if anything is unclear to you.