if you're looking at the "all in one" (AIO) you are looking at the Elementals. The sewn in soaker (which is what makes it an AIO) is all organic material. The outer shell is made of PUL (poyurethane laminate) which is what makes it waterproof. It is one size (OS), which fits about 10-35 lbs (depending on the shape of your LO). Is this it? http://www.nappyshoppe.com/store/bumgenius-elemental-ones...
You will need about 10-12 diapers a day, depending on the age of your LO (the younger they are the more you need). If you plan on washing every other day, you will need 24.
Here's a helpful link to my local cloth diaper group's page, which has washing info, as well as different types of diapers.
http://dfwclothdiapergroup.weebly.com/cloth-diaper-info.html
I will mention that I have heard good things about these, however I have not personally used the Elemental. I have used the BumGenius pocket diaper and their old discontinued AIO diaper (it was sized and had a sewn in microfiber insert). They are fine, but not my favorite. But, I have tried a LOT of diapers, so I have others that I have found I like better. The BG's are great for my DH and also casual caregivers (grandma's) to use, since they have hook & loop (mine do, the ones I think you're looking at only come in snaps).
I will suggest you try 1-2 before investing in a full stash of one type of diaper. When I started I tried a few different kinds to decide what types and brands I like best before spending the money on a lot of one brand. If you prefer, you can have only one brand. But don't feel like you have to. It's perfectly fine to have a few of several types and brands of diapers.
If you are new to cloth diapers, one that I love (and think is great for CD beginners) is the Thirsties Duo Diaper. It is a duo size, similar to OS, but siaze 1 is 6-18 lbs, and size 2 is 18-40 lbs. This ensures a better fit. The inserts (one microfiber and one cotton/hemp) agitate out in the wash since there is a pocket in the front and the back of the diaper, so no need to take out the wet/dirty insert prior to washing (like most pocket diapers). It's very easy to use, and super cute! http://www.thirstiesbaby.com/duo_diaper.php
I work at a CD shop and the Thirsties Duo Diaper is a huge seller! I have a couple and love them. My LO can even wear it overnight with no leaks, and he still BF's 2-3 times a night (with an added insert http://www.nappyshoppe.com/store/gflapper-™-insert-hemp-.... I'm actually about to get more and start using them as his night diaper.
Message me if there's anything else I can help you with! I've been CDing a little over a year, and LOVE it!! I've become somewhat of a CD expert and love helping people get started:)