Hi lailah,
I recently stayed at both the BWI and the AKL. I absolutely loved the BWI for it's comfortable size, central location, great food options, wonderful staff, and lovely surroundings and views. I found it offered much more than the AKL.
The boat is slow but pleasant. When we were there in mid August, there was approximately a 15 minute wait between boats. It goes from Epcot - BW - Y&B - S&D - MGM and then back. This makes it around a 20 minute ride to MGM once you catch the boat, but a short ride over to and from Epcot. We never took the boat to Epcot though since it a pleasant 5-10 minute stroll. Unless the boat is at or coming into the dock, it is quicker to walk. Coming back from MGM, we would get off at the Swan and Dolphin stop and walk back to the Boardwalk (again around a 5 minute stroll, so we would beat the boat by about 5 minutes). If you just miss the boat going to MGM, you can hurry over to S&D and pick it up there. If you do want to limit your walking, you can do so with a little patience.
The buses are also shared with the other Epcot resorts. The order of pick-up is often Swan-Dolphin-Yacht-Beach-BW. When it's busy, buses are dispatched to handle the load, so that not as many resorts may be sharing. It is generally pretty quick getting to the parks from the BWI since typically the bus will go directly to the park after its BWI pick-up. Returning from the park you are likely to have to wait through 2-4 stops. Again, a possible option is to get off at the Swan and walk back to the BWI.
HunnyBunny addressed your food question. The BWI restaurants are the Boardwalk restaurants, and they are quite convenient. You can get room service, but otherwise, I believe you must physically exit the building to reach all the restaurants. We only tried the Bakery and Spoodles, and we loved them both. For more information, you might check the menus on wdwig.com.
The main pool is very festive. The slide is probably much too big for a 3 year-old though. Since my son is older, I can't really evaluate the pool for a young child.
You will love BWI. It should provide lots of entertainment and dining options for you and your granddaughter. It's lovely and has a great central location. The only thing missing is monorail access to MK.