You don't have to gut load flies, keep the pupae in the fridge and hatch out 10 at a time. They will keep for 2-3 weeks. They are a pain and make a mess if you feed them.
You should be able to get superworms and maybe calciworms from a local pet store. Depending on where you are , you might have access to other feeders. I don't locally, so I have to order online. I also raise snails and I'm going to try raising isopods again. My Jax enjoys both of those.
For the crickets, mix in carrots, turnip/collard greens, butternut squash, apples, peppers, and other stuff. I blend it up and freeze it in an old ice cube tray. Very easy and keeps forever.