Feed small mealworms and small crickets starting 3-4 days after hatch (they won't be hungry right away because they are still getting nutrition from the absorption of their yolk sack). Mealworms can be left in the enclosure at all times and supplemented with crickets or other insects several times per week. Also keep calcium and fresh water available at all times.

You can house clutchmates or pairs together until 4-5 months of age (females of course can stay together indefinitely depending on the enclosure space). Leos are sexable at about 4 weeks, so you will be able to tell males from females, but you don't have to separate males at that time.

Keep hatchlings on moist paper towels and mist once or twice per day for several months. In a shoebox rack system you will not have space for a humid hide as they grow, so you can substitute for this by misting once or twice per day as needed. When the geckos are older and moved up to larger enclosures with humid hides misting is no longer needed.

Fat deposits behind the arms are normal and a good thing. There is no reason to want your male to slim down. It is not likely that you have an overweight male unless you are feeding excessive amounts of pinkies (males don't need pinkies at all and females don't require them, they are just a good way for females to put weight back on after each clutch--one pinky fed after each clutch is laid).