You might get away with a 3ft if there is a lot of cover and hides. A lot of people start off with faunariums or storage boxes for hatchlings as a large open space can make them feel insecure and you might struggle to get them to feed. When it's adult you will have to see how big it grows to determine the size of the viv for the rest of it's life. As for heating a heat mat would be used on half of a faunarium/box and in a wooden vivarium a heat mat, ceramic or a light bulb - its personal choice really but you will want to keep temperature up at night so a light bulb only might not be the best idea unless you get a red bulb for the night time.
Thermostats - you can get on/off thermostats which turn off when it rises to a certain temp and on when the temp drops below a certain temp. You can also get pulse thermostats, which I prefer because they are more accurate at maintaining temperature, which send pulses of power to the source of heat and so will give out less heat when less is required. Dimming thermostats are similar to on/off but the power 'dims' rather than just switching off.
As for substrate a lot of people I know use aspen but again its really personal choise as to what substrate to use so long as it hasn't got anything in which is toxic to reptiles.
humidity should be kept relatively low (your heat source will help with this) around 50% but make sure the humidity is higher during a shed by spraying or providing a box with spagnum moss in.
Prices around my area usually ranges from around 70-140 for a normal and obviously more money for a morph.
I don't have snakes of my own so I'm not very experienced or knowledgable on snakes therefore I hope this gives you a better idea and that more experienced people will see this and give you a better response.
For other information it's a good idea to buy a book and look up caresheets like these: http://www.barrieranimalcareclinic.c...%20pythons.pdf
. Constantly research before you get your snake and you'll be fine