Just some thoughts...
I know you said you could only get those huge crickets but your little Leo won't/can't eat them. That could be part of the trouble.

I see you are looking at freeze dried alternatives, Leo's like live food. I have honestly never heard of anyone having any luck getting a Leo to eat that stuff.

If you can't get small crickets (or don't want to keep them) then try mealworms, they are a fine food and are easy to keep. You can just put some in a small dish and your Leo will eat them from it, just change them out daily so they are fresh and gutloaded. Keep them in a mixture of oats, wheat germ, dry milk, baby rice cereal etc., good stuff...your Leo is what it eats If you just leave them in the bedding/gutload they will eventually start breeding and you won't even have to buy them anymore!