You have to see his demands by observation for the eating schedule, so use a cricket keeper with gut load (green cubes) so you never keep loose crickets in the cage for any length of time. Usually I feed at night when the lights just go off and go from 5-10 large crickets per feeding, trying to give all that they can consume. Every 2-5 days is a good feeding schedule, at times I have gone 7 days due to my work schedule and has not effected their health. I can say though, it has effected their breeding cycle, so closer to every three days seems to be the best. He will get his weight up if conditions are right, but offer a few (5 or so) wax worms on a tray every night for a little while along with dusted crickets.
Also, due to shipping issues with Indonesian species, get him the water bowl and possibly offer a light misting for him to lick off his face as he could have slight dehydration, he does not look too bad though compared to others I have seen. I lost another trio due to dehydration issues on import and I did everything right.
As for weight, these geckos come from a vast habitat with likely many variants, species and sub-species of different size and fairly little study. I would not be concerned with weight, if you get him the food, water and right living conditions he will live a long healthy life. They are thin geckos, but you will notice him bulk up more than he is now.
Here is a picture of my male and size to compare, and honestly I think mine could use a little weight in this picture...
