There is a couple ways to feed cresteds, they typically feed daily as adults but can be feed every other, or 3 times a week. Juveniles should ALWAYS eat everyday
A geckocan typically eat 4 to 5 crickets at a time(each individual is different)somepeople like to put crickets in at night and take them out in the morning where as some like to only keep them in for a half hour to an hour but i personaly just leave them there(i don't have anywhere to put them). As for the size of the crickets it depends on your gecko(nothing bigger than half there head they might choke) like mine doesn't eat them that well but they can always eat powdered food mine eats Zoo Meds Day Gecko Food and Reptocal for calcium, he also loves mango baby food. They can also eat overripe or mushed tropical fruits.