Carol, I think it is wise not to have the worms too deep. I probably have mine full a little more than 1 1/2 inches but I try not to put too many in a container because they start dying.
I just throw in some oatmeal or cornmeal. Their bedding is also their food, Nicole so you don’t change it at all. They will eat it all up if they aren’t in the fridge. Now, if you are growing mealworms you’ll have to change it because their frass will build up and there will be more frass than food source.
I try to keep my mealworms fed so they are more nutritious? I’m not sure if that’s how it works but that’s my thinking. I keep them all in the fridge because I buy them in quantities of 5000 and they start pupating on me if I don’t.