Welcome to the site!
If your looking into ball pythons you've sure come to the right place.

A twenty gallon tank will hold an adult, but I can't stress it enough how you need to grow your tank with the snake. Pet stores aren't very good about this.
If you intend on ever getting a baby it will probably need to be put in a 10 gallon or so.

They are not difficult but do need a bit of work and expense more than corns do. Corn snakes are also not nearly as specific about heat and humidity controls as balls are.

Let us know if you have any other questions and feel free to ask any of us if you want to know anything specific! :]