What would I need to care for him?
The 20 long will work. I know 10 and fifteens are about the same hight and several breeders keep single animals in those cages.
The care is generally the same for cresteds.
Are they harder to care for than Leopard Geckos?
Not at all, and they might even be easier. They do not need any supplemental heat if your room stays between 65 and 80 normally.
What type of fruit will they need to eat, and how often?
They enjoy bananas and necter fruits like apricots and peaches. These are easiest to offer in the form of pureed babyfoods.
Can they eat any other insects besides crickets, such as mealworms?
They can eat freshly molted mealies if they accept them.
What kind of substrate should I use? With leopard Geckos, all loose substrates are a risk of
impaction. Is the same true with gargoyles?
Any substrate has risks including papertowels if accidentally eaten. My leos regularly consume the substrate in there laying box and regularly pass it. Many Rhac keepers use loose substrate without problems, though I have heard of a problem once on thes forum involving a hatchling crested. Milled coconut husk works as a substrate as do topsoil blends. The Rhac book suggests this substrate: A potting soil mix where the main component is either peat moss or ground fir bark. It must not contain perlite, fertilizer or pesticides. They mix in 5% sand and 15% fine orchid bark. de vosjoli goes on to talk about creating a biologically active soil by regularly stirring up the soil to mix the feces into it. If this is something that interests you, I would pick up the book or email me and I can elaborate more.
Lastly, another feeding option is using the Gargoyle Gecko Diet developed by Allen Repashy, and distributed by T-Rex.
good luck
-----
Bill DiFabio
Azteclizard.com
Email Me