Ok, I'm not trying to start anything but what gives?
You post over in the burm forum, and don't like the advice, so you come to the ball python forum and post the same thing?
Look you might get away with a Human heating pad(hell I got away with it for a year or so till I knew better)Some people get away with one forever!!But alot of people don't get away with it.Why would you want to take a chance?
In your other post you said you only had $400 to put into this snake, right? $400 will go fast!!You said you don't have a job and no way to get any more money, right? How do you plan on feeding him? Are you going to breed your own rats? If so how will you feed them? (now I raise my own rats and I get feed from a fram store, but I have heard you can use old roy( I think that's what it's called) dog food, it's real cheap)This snake is LONG TERM!! Feeding him as you should will cost alot and what if you need a vet? They are not cheap.
I see what you meen about not getting a cage right now as he would out grow it fast, your right he would, but even a cheep "Sterilite" tub would be better then a FISHtank. I'v used fish tanks too, And as a temporary holding tank I still use them.
Why don't you do this, Build The large cage now but add a devider, that way the cage is not too big for the snake now, and he can grow into it, instead of growing out of it.
You still need to think of how you will feed him, and when he gets big you'll need to find rabbits.Trust me I'v had burms and other large snakes for over 15 years, One thing they do great is eat!!
You can get some good advice here, but you got to listen to it.No one is trying to make you look bad, they are just trying to help you.