BP's are pretty good at escaping, you will need to have something heavy on top of the cage top or a secure lock if the cage has front opening doors.
How big of a cage are we talking? The general conscious is that a small cage is better, but personally I have found that not to be the case (as long as you don't go crazy). I've had success with hatchling BP's in cages that are 24" x 24" x 12" (L x W x H), but keep in mind that larger cages are harder to maintain (heat/humidity/clean) and you will have to do more to make sure that your BP feels secure.
I don't see why you couldn't put pothos vine IN the cage, but not draped into the cage from outside the cage, as you need a very secure top to the cage. (1/4" wire mesh or smaller)
Pothos vine comes from a very different part of the world than BP's. You will probably have to use supplemental lighting for it to grow (never put a snake cage in direct sunlight as it will act as a greenhouse and get really hot inside) Plus BP's are know to smash plants up pretty bad.