Need help making rack for my BP's

[Duke82]

I will be getting 3 ball pythons from a friend who breeds them in a couple days. They are around 2 years old I think. The questions I have for you guys are. Do they get stressed if they are in to big of a cage for there age/size. I only ask because I went out and bought 41q 35 X 16.5 X 6.125 sterilite bins for them. I did this after reading they need the space but did not put 2 and 2 together till just now that maybe they will do better in smaller cage till they get bigger. Also I planned on using flexwatt tape for heating on a thermostate, any tricks of running that. I have 3 strips that are 6ft long and 3.5in wide I used to use them for my roaches when I had alot of beardies some years back. I was planning on running 2 strips on each side. But not sure if I should put some aluminum foil or something inbetween the plastic and the heat tape. Sorry for such a long post.