a 10 gallon set up will work just fine. The only possible issue that you will have with belly heat is the fact that most of the time neonates / juveniles are pretty arboreal and will tend to want to stay up high. You'll need to keep his setup pretty simple at first, give him a bowl of water, and maybe a PVC perch. If your air temperature is really cool, you may want to consider a different form of heating in order to increase your ambient temperatures as well... now, on the counter side of things. You can do OK keeping it in a rack system as a neonate / juvenile. Because of their arboreal nature, people tend to stay away from such a shallow tank, but in most cases they will do just fine without a perching system. If offered one they will typically use it, but if not offered one they won't get stressed to be honest.

Make sure you can get your abients to around 82 degrees on the low side for the warm side, and a basking spot around 88 generally works out pretty well. Keep its susbstrate simple until you get at least a few meals in it though. And don't worry about sustaining this massively high humidtiy in the cage, just another thing people tend to over do when it comes to carpets.