We always do BAB EE! My kids are so shy and they were just overwhelmed at the "regular" crowds so it has been the best for us. You can do it staying at all 3 resort hotels and you can make reservations up to 30 days ahead by calling guest services for your hotel. I usually just call the hotel main number and ask for guest services and they transfer me to the right place. A few times I have gotten a new CM who didn't know what I was talking about but I was persistent. Twice we went and they did not have us on the list but I had gotten the CM's name who made the reservations and had it with me so there was no problem. They only take a limited number of participants, 10 or 15 tops and usually there are less than that. Once, in Jan, we were the ONLY ones and it was so cool to have the whole store to ourselves. I think most people wait until they get to the hotel but I heard people did not get in the day they wanted and never took the chance (I am a planner-lol.) Usually, it is 2 or 3 days a week but it changes so I am not sure now what the days are.
There was talk about a "minimum purchase" at one time but no one has ever made us pay ahead or taken a credit card # or anything but we usually do get new critters. We have just gotten new outfits on occasion though and nothing was ever said then either about a minimum purchase. (Really figure $100 for 2 kids though by the time you pick an animal and an outfit but there are $5 off coupons around too and they do have a card for "frequent buyers" that is worth doing it you go enough to get a discount after X$)
Since we had APs, we usually did it on Sat morning followed by a character breakfast at Goofy's and a afternoon at the pool rather than buying the $30 block out pass. This is my FAVORITE but a good second is to do it on the day you leave. We do the same: ee BAB then Goofy's then the long trip home with new "babies" and full bellies! Even the slowest child will be out in time for a 10am breakfast reservation.
Pay attention to the signs as you walk by or check out the BAB website for new releases or promotions when you pick the date to go. If your kid wants a special one that does not get released until Friday and you have reservations before that, it will be saaaad. They will not let you have it before the release day but almost always have it in the back to "preview' before your bab day. Sometimes they have specials, once the kids got little radios or other "free with purchase" items like babies. As EE BAB participants, you always get a few extra goodies like the brush the other poster mentioned as well as a bunch of stickers. Also, it you lose your bows, don't hesitate to ask for a few replacements. They have a giant box up at the register. Once I asked for one white one as dd had lost hers and they gave me a handful of all colors!
Have fun!