I would definitely keep him in a rubbermaid for now, especially since he's young. That way you can make holes on all sides of the rubbermaid so there is lots of cross-ventilation. It also makes it easy to put in lots of branches the way you want them. Use papertowel substrate (at least for now, until you are sure the snake is mite and parasite free. even then you can keep using papertowel), and give her a snug hide (upside down ceramic or plastic pots with holes work well). Offer a couple hides of different sizes if possible. Also give her a big water bowl, under or over the heat source to increase humidity. You'll also want to spray once a day, probably in the evening when it starts to get dark. Keep a 12/12 day/night light cycle because they are from equatorial regions where there isn't much of a daytime duration change throughout the year.
Provide the snake with lots of branches of different sizes (make sure you scrub them with a mild bleach solution and a scrubbing brush - rinse them well and let them dry before using them). You should also give the snake plants. You can use live plants like pothos, but you'll have to make sure that your snake isn't in the plant when it eats in case it gets dirt in its mouth, or you can fill a vase with rocks and water and just put vine clippings in there.
Fake plants are great, too. Some even have suction cups so you can stick them to the side of the rubbermaid. I hear atbs like those. Or plastic vines just strewn around the cage. Make sure it has enough foliage to hide.
When it gets older you'll want to get a custom cage made, tanks are no good for arboreals.
As for the atb itself, I would be wary of petstores. 59$ is a good price, but since you're getting it from a petstore my bet would be that it's WC. For a first time atb keeper, I would steer very clear of a WC atb, because you'll end up spending more on meds to clean up the snake and you may have to deal with fussy eaters, bad shedders, etc etc. You'll be far better off buying an established atb from a breeder. You'll have a bigger choice of snakes, and sure you may be spending 50$ more but you'll save tons in vet trips and grief and stress.
However, if the pet store atb looks cb and healthy, go for it, but be wary and try and find one from a breeder instead.
I think that covers it! There are a million caresheets online, here are some of them:
http://www.compasscomputers.net/boa-cam/ammycare.html
http://www.corallus.com/urbanjungles/ammycare.html
http://centralpets.com/pages/critter.../SNK2744.shtml
http://www.reptilekeeper.co.uk/amazonboa.php
http://thompsonsden.tripod.com/careofyourboas/id2.html
http://animaldiversity.ummz.umich.ed...lus/c._enydris$narrative.html
Read them first, they will help you perfect everything. I also suggest you regulate the temps and lighting before getting your snake, so you don't have to stress it out needlessly with playing with UTHs or lightbulbs or whatever.
Oh! And make sure, if you use a lightbulb to heat, that it is NOT in the cage. You don't want the atb striking at it and/or coiling around it and getting burnt.
Zoe