Your supplementing sounds fine as along as he is under standard UVB lighting, T8 5.0 or 10.0.
As for feeding, you could increase the amount of food as he isn't going to get fat overnight. I would allow him to eat a little more and just keep an eye on his weight as he gets older. Also, I would add more variety to his diet. I would throw some Silkworms, Hornworms, Crickets, etc. into the mix.