No it's not guaranteed that a newborn will eat. Fortunately all 6 of mine have done tremendously well. I still have a few that are not great cricket eaters, but that is not necessary to their diet. Anytime I was unsure that they recognized the Crested Gecko Diet as food, I just put some in a small spoon and dabbed a bit on their nose. They'll lick it off, and you just got food down. I'm sure there will be the rare hatchling that just wasn't meant to make it.

As for breeding. Females lay eggs two eggs (typically) per clutch, and will lay several clutches. Mine laid 3 clutches, hence 6 hatchlings. My last clutch is only 3 weeks old, and doing well. The only way to control the mating is to separate the male and female.

I hope that helps.