A neonate would likely do best in a six quart tub. You just need to add perches, and holes as needed to control humidity.

For the heat source, you could use flexwatt, but a better option is an ultratherm, like on this site: http://www.reptilebasics.com/ultratherm-heat_pads/. However, the ones on that site would be to large. I found one at the pet store that fit perfectly. It was made for a hermit crab cage. You would tape the ultratherm to the back of the tub using foil tape, as opposed to the buttom, since the snake is not going to be sitting on the bottom of the tub.

Once it gets a little larger, you could move it into a fifteen quart tub. At approximatley a year old, you could move it into a 2x2x2 arboreal cage. I bought mine from http://www.pvccages.com/, and am very happy with it. I bought the 2 foot cube complete setup. I just added some additional plants for added security, and visual appeal. The cage comes with a radiant heat panel, but you will need to buy a digital thermostat. I suggest Spyder Robotics Herpstat.

Hope this helps.