The four foot cage, I would run 11" heat tape at one end from front to back, so 2' in length. The door style is mostly preference, and I like sliding glass usually. The single piece doors are alright, especially with good tempered animals. I prefer black cages because they don't show the stains of newspaper print as easily as white. But, white cages allow you to notice things like mites a lot easier than the black. If I only had a couple animals and I was going to do a more natural looking cage, I would probably just go with the color that best matches the room the animal is kept in. Nice looking Dumerils!