Fuzzies are too small. For future reference, I wouldn't buy from a seller that has no knowledge of their weight or food size.
To make his tank seem smaller pack it with as many hides, wood, fake plants, etc as possible. Can he creep from one side of the tank to the other without being seen? If not, add more clutter. Try digging up the substrate to make a "burrow" and putting a hide over it. In the wild they will hide in pre-made burrows like that. You want to make sure the BP feels as secure as possible.
Also, the substrate temps don't matter. You want to be measuring the surface temps because they can and will burrow.
Any chance we could get pictures?