Hey there,
first of all, if you want to get this little guy growing and living well, I'd suggest putting him in a bigger terrarium. At least a 20 gallon at this point. Horned Lizards get stressed very easily, and a small enclosure isn't good for them.
When he gets to be an adult, you want to think about putting him in a 40 gallon tank, and even this should be considered the bare minimum. My opinion has always been that HLs thrive best when living outdoors, but as Winter approaches, not a good idea.
Your idea with a hide is good, HLs need room to escape the heat just as much as they need the heat; hence why a bigger tank is a good idea. One hot side, one cool side. The lights also sound ok. The sand level is good, but you might be able to add some without hurting the look of the enclosure.
At this point in time, your HL may be preparing for hibernation, which means it really won't be doing much in the way of anything. To be safe however, make sure he has water. You can lightly mist the actual lizard in the morning with a spray bottle, and it should drink. Also, if you don't, offer a water dish. Sometimes they'll drink from that. You are correct in their feeding habits. Ants are non-negotiable for healthy HL husbandry. Since I don't know the locale of your lizard, its hard to say what type of ants are acceptable. Keep in mind, feed one or two ants at a time though. More than this will likely stress out your baby. Go to a field, and find an ant nest and just pick up the smallest harvesters around. Chances are there are plenty of varieties of ants around you,
so use good judgement. If all else fails, there are ants available online. Type Horned lizard food in your search function, and you should get some sources. I hope this helps you, and good luck with your new HL.
-Phil Clevinger
