Well the basking spot should be about 100 degrees at one end. The other end should be about 85- 80 degrees (the higher one for babies).
At night the ambient temperature should be 75-80 degrees (again the higher end for the smaller ones). You should also have a full spectrum light bulb like repti-sun 10.0 or something like that. Since it’s a pretty big tank I recommend at least a 100 watt basking lamp. If you don’t have enough calium and vitamins they can get metabolic bone disease.

About the spinach, don’t feed them that! They contain high oxalates which can bind calcium. Collard greens, Kale (only sometimes), cabbage, spring greens, escarole, turnip greens,dandelion greens, parsley, carrot tops, and mustard greens are a good veggie source. Some strawberry can be given as a treat I’ve heard. Try feeding them a mixture of these for a good nutrition. As for the small crickets, you should put lots of them in there and wait about 10 minutes. After that remove almost all of them leaving two or three. Don’t feed them mealworms for they have a hard exoskeleton which can cause impaction.

As for substrate, yes, sand can get bacteria easily. And it can also cause impaction. Try using something called Excavator or something like that, which is burrowing clay. You simply mix it with water then mold it the way you want it. I say you leave a hole under the cave you should have creating more space for them.

Hope this helped!

The best substrate would be a non-particulate one. You have some options here. You can get textured slate tiles from Home Depot, Lowes, or another Home Improvement type store. They’ll even cut them at the store to a size that fits your terrarium, and they are fairly cheap. You can get reptile carpet at most pet stores, make sure you get the kind that doesn’t have lots of loops that can snag claws. Just ask at a couple pet stores and they should be able to show you some. You can go to a normal type of store and get non-adhesive and textured shelf liner, and go with that. Or you can just use paper towels. All of these options are safe, and all but the paper towels are fairly attractive as well.
For the best diet, I would up the amount of feeder insects you are giving to 30-80. What you want for salad is rich healthy greens like Collard Greens, Mustard Greens, Turnip Greens, Dandelion Greens, and Escarole. Then mix in some vegetables, like squash, asparagus, etc. and a couple of times a week feed treats like strawberries or other fruits. Here is a list of good salad ingredients and how often to feed them: http://www.beautifuldragons.503xtreme.com/Nutrition.html
First, you need to fix the thermometer problem. You want a digital thermometer with probe. The low 100’s temp everyone is talking about is the temp of the surface of the basking area. You want that 100-110, and you’ll be measuring it with the probe part of the thermometer. Then you want a cool side for them to be able to retreat to, that can be anywhere from 70-85 degrees.