s far as your cage goes I would something for more floor space than height. You could ask a lot of people on this forum and they'll tell you that using tubs (think sterilite or rubbermaid sweater boxes) is practical and functional. It's not the most beautiful display set up, but works well. Paper towels, newspaper, shredded aspen, coconut husks, and repti-bark type substrates all work well. Some, such as hold more humidity than others, so that is a good factor to consider. But if you go for a tub set up you shouldn't find it difficult to control the humidity inside.

As far as buying a snake from a show, make sure you shop around and ask lots of questions. Look for a good and fat well-started snake that has successfully eaten on its own more than once. The more the better. Ask if it was captive bred, wild caught, or farm hatched. As a beginner, you should probably go for a well-started captive bred animal. Ask for feed/shed charts, a lot of reputable, responsible breeders will have these available. As stated, ask a lot of questions and don't base your purchase soley on the price of the animal.