I get the crushed walnut shells. Safe and not as dusty as sand.
http://www.pets-warehouse.com/pic-s/SCLRP211.JPG

KSBs are fantastic. That size of a cage isn't needed for a male though, a female would be fine in it. A 10gal would be acceptable for a adult male KSB.

If you come across any KSB breeders online let me know. I'm looking to buy one too, as a good friend of mine has one. :]

Edit: Well, its not necessarily a very good starter snake because its a bit hard to handle? It gets scared when its up high and holding them is awkward at first because they move differently than any other snake.