First, it is great to ask questions but just remember, no one will know your snake better than you. So, irregardless of the advice you get on this forum (so great, some outragious), do what you feel is best for your snake. You will know when your snake is hungry, when it is not, when it is irritated, when it is calm, and on and on. By cueing into your burm's subtle cues you will essentially become an expert at YOUR snake's natural behavior. With that being said, when it comes to feeding, let the animal's behavior dictate what it needs. I would recommend feeding several large adult mice every week but at the size this burm is at, you can try a small rat and see what happens. The sooner you can get the snake on rats, the better (for burms). You will see rapid growth rates and when the snake begins taking rabbits (if you go this route), well, watch out. Some of my adult burms prefer jumbo rats over rabbits so that is what I go with....once again, I let the animal's natural behavior tell me what they need. Hope this helps.
In regards to your caging question, if you think it is a good deal, then that is all that matters. Sounds like a decent sized cage for an adult male burm (and your choice to use pro product heat panels is a very wise one). Remember, even though males usually reach smaller sizes from females, they are capable of reaching large sizes....I have seen 16' massive males.