S.B.
I hadn't heard of the 4.0's so I had to look them up... We use the 3.0's and love them. They look to be essentially the same diaper with the exception that you now have a choice between snaps vs. hook and loop tabs. I've had my son in the 3.0's since he was about 2 months old, although I bought them before he was born. They were too big for him right away (he was 6 lb 4 oz) so we had to wait a bit for them to fit him.
I purchased a simple diaper pail and liner (wet bag) from the same website I got my diapers from. You do not need to soak your diapers at all, in fact it is recommended to use a dry pail. For pee diapers, I separate the insert from the cover, fasten the tabs to the laundry tabs, and toss everything in the same pail. For the poop diapers, I shake the solid poop into the toilet, rinse the diaper cover, and put all in the same pail as the pee diapers. When the pail is full, I machine wash twice (once on cold and once on hot) with an extra rinse and hang dry. Sidenote on poop diapers: When my son was tiny and his poops were not formed, I still rinsed the diapers well and scrubbed out the elastic creases (like around the leg holes) with an old toothbrush. I found that if I did not do this, the wash would not get all the poop stains out of the creases. I still do this when any poop sticks to the diaper cover, because I do not want that sitting in the diaper pail.
As far as snaps vs. hook and loop... I've never used snaps. With hook and loops, I've never had an issue. They are highly adjustable, easy to use (very similar to a disposable), and durable (been using same diapers for over a year with no complaints). I am finding that my 16 month old son is starting to want to pull at the tabs if he is not dressed, so I keep him dressed so the tabs are out of reach. He can't undress himself yet, so that works. I'm not really sure that snaps would make that much of a difference though, because I believe that if he wants to undo it, he will find a way, lol.
I think you'll like the bumgenius diapers. I got mine from cottonbabies.com, and if you go to the site they have a lot of information about cloth diapering, including washing instructions and all that jazz. I like this site for buying above others because they give you a choice on the colors of the diapers you buy (you can get a pack of 12 and choose the color for each one!) and they have a good selection of accessories as well. They sell more than just bumgenius brand, so you can compare different types of diapers if you're still undecided.
Happy diapering!!