There are many choices when it comes to housing a baby boa. You can go with a glass tank, plastic tub, or a pre-fabricated enclosure like the one you put a link to.

If you can afford it, you could go ahead and get the adult sized enclosure right off the bat. Although I don't normally recommend this, you can get away with it if you furnish the inside with enough hides and accessories to make the snake feel safe. Boas aren't normally prone to severe stress like a BP, but you still need to make sure that they feel secure.

Be aware that Boamaster enclosures are made of wood and are extremely heavy. I have heard good things, but they are a pain to ship. There are many companies that make PVC enclosures (Vision, Boaphile, Beeger Boxes etc) but they are going to be significantly more expensive.