Congrats on getting the little guy and doing right by him to get him fixed up and in the right direction! I will say that tubs are MUCH easier. I have three and two are in tubs (rack) and one is in an aquarium in my sons room. The aquarium can be a real pain in the rear end to clean, disinfect and maintain temperatures.
As far as the light/lamp goes.. I would say move on from that and use under tank heat with a proper thermostat to control the temperatures. Just make sure you have an thermometer to check the temperatures to make sure they aren't too hot.
Substrate.. I have always used aspen.. Its a bit more work than a coconut husk but it smells good, cleans easy and the snakes have always shed well for me..
Finally, the tubs will help you with humidity tremendously.. Tanks are hard to maintain that without misting and covering the warm side.
Best of luck getting this new guy back to happy and healthy.. Sounds like you are well on your way..