The best bet for just starting off is to use a commercial gutload, anything by Flukers or we really like the Yummies brand (both available in national chain pet stores). Pick a gutload that is both food and water and you'll be set. Dust any prey items in a mineral and vitamin powder, preferably one designed for leos.
I'm not sure if you mean the geckos or the crickets will overeat? Prey items won't over eat and leos should be fed as many prey items as they will eat at one time. Removed uneaten bugs unless you have a bowl to keep the mealies in.
If you are new to geckos then I would suggest you pick up a copy of the leopard gecko manual at the very least. It will tell you all you need to know about temps, feeding, prey items, behavior, etc. You can also find answers to all the questions you asked today by searching this forum.
As for handling them: I would not try handling them more often than once a week initially while they grow and settle in. It takes a lot of patience and time to hand train a gecko, but they are wonderful pets. There is a post by the user named "olstyn" a while back with very detailed information about how to train a gecko and I would suggest looking that up as I don't have anything could add to it. Good luck.
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0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock