It varies a fair bit on the individual snake. If you can find a captive bred one that feeds well on dead food you are much better off. I have keep legal wild caught and captive bred, not all of them will eat fish. One of my wildcaught males wont touch them but was easy to get feeding on dead food such as geckos, pink and fuzzy rodents and hatchling quail.
They are extremely fast and flighty, you need to be really switched on when handling them, especially little ones. Even experienced keepers have lost hatchies due to their speed. They can also hurt themselves from thrashing around if you dont hold them properly (so im told and i wouldnt doubt it).
If really stressed they use a stink defense thing, but they have to be really stressed to do this and it rarely happens if you treat them nicely.
They are more like a very fast active lizard as far as keeping difficulty. Nothing like a python at all.
A 4' fish tank seem like a good size enclosure for an adult, but more height would be good. Plastic tubs over 100l are also OK and allow for much easier maintanace. Like most snakes they can eat each other, so the safest option is to keep them seperate.