The enclosure you got is fine for a subadult to adult crested although if the gecko you got is a hatchling or young juvie it will do better in something smaller like a kritter keeper so that it can more easily find its food.

Paper towels are great substrate (the best IMO for cresteds). I do provide hides on the ground for my cresteds--some use them and some don't.

Cresteds do not need any sort of supplemental lighting unless your temps are below 65 and you are using it for heat. Even then your temps should never get above 80--cresteds need temps between 68-78.

Humidity of 60% is just right. You should mist once or twice per day for humidity and also so that the gecko can drink the water droplets. Make sure the enclosure dries out between mistings in order to avoid mold growth.

I'm not sure what the person in the pet store meant about fruit and meat unless she was talking about mixing baby food together, but baby food should be avoided as it is very high in sugar. You should feed the T-Rex crested gecko diet, which you mix 2 parts water to one part diet. You can purchase the diet here: http://www.pangeareptile.com/products.htm#superfoods.

Insects are not required but most cresteds like them and enjoy hunting them. You can feed crickets (the length of the cricket should be no more than the width between your gecko's eyes), Phoenix worms, silkworms, feeder roaches. Mealworms are not a good choice as cresteds cannot digest their chitinous shells, thus they serve only as filler and not nutrition.