I agree with the above, 10% is too much for your little guy.
He is hiding because he has not gotten used to you and his new home yet.
You have only had him 4 days, he needs lots more time.
They usually explore their new cage when you first put them in. That's why you could see him, he was still in the
process of looking for hidding places. So by the 3rd day, he found some good ones and you havent seen him since!
that's pretty normal
It can take a while before he comes out of hidding and realizes that you are not a preditor about to eat him!!
Look at my old posts on this subject of acclimation.
When he comes out in the open to bask and will eat in front of you (he knows when you are watching, even if you dont realize it) then you can start hand/cup feeding.
Make sure he sees your hand every day for feeding.
I would feed him about 10 crickets, maybe throw in a few more if he wont come out when your around and you have to "free range" hunt the crick down method.
For the acclimation time, you may not know how many he is eating, or if drinking, so watch for his poops.
Make sure they are dark color and solid and there should be a seperate white part called urates (lizzards dont exactly pee!!).
As long as you see this, he is getting what he needs.
The key word with a new cham is PATIENCE!!
As for the UVB, you want a 5 to 6% Arcadia HO w/ fixture (my top choice), or a ZooMed Reptisun 5%.
Make sure to buy a tube style, not the compact type.
Also, make sure he has total dark at night (no night lites!!)
They need cercadien (spelling!!??) cycle just like us
Lets see some pics of your new guy