I will try to answer the above questions.
We did eat in The Mara, and we did like it. I had the flatbread pizza a few times, and we had breakfast there a few times. My son has food allergies and they were great about accomodating him. The selection is not as extensive as the larger food courts (pop century, caribbean beach, etc.) but is about on par w/ the Grand Floridian quick service restaurant. Decent quality and the prices weren't too outrageous.
The pool slide was okay, it is kind of small so it isn't really a thrilling ride or anything, but the view from where you get on the slide looking over the pool area is pretty cool. I did see several kids going on the slide over and over, so they must have really enjoyed it. They were about in the 6 to 8 year old range.
We were travelling w/ a group of 7 and my brother and his girlfriend slept on the sofabed. My brother is 6'4" tall and his girlfriend is petite. They said the sofabed was fine. I would think that my brother has a hard time getting really comfy in any bed, at his size, so the fact that they said it was fine was probably a rave review

plus they shared a room w/ my parents who snore and they didn't get a lot of sleep because of that reason.
My overall experience at AKV (it was our first time at this resort and first time as
DVC members) - we loved the resort. It was gorgeous, the pool area was very nicely landscaped and the resort overall was done very nicely with the african theme. There were lots of activities for kids if you wanted to get out of the sun. The studio units were very lovely, in our opinion, and being newbies to DVC, we very much appreciated having the kitchenette. We had a savanna view and saw lots of animals, though I think more were visable from lower floors because the trees kind of block the view. We enjoyed room service a few times and the whole experience just felt very luxurious and relaxing. It was very quiet and almost serene. We ate once at Boma and enjoyed that although buffets are not my favorite. The bus service was excellent. We didn't hear or see any construction except for a crane in the distance and some black draping covering parts of floors 5 & 6 from the lobby. The valet parking was very convenient and it was a nice perk to have that be free. The only downside to our experience at the resort was the cast members didn't seem knowledgable about DVC in terms of the housekeeping options. I wanted a trash and towel service every day and knew I had to pay for this but everyone I spoke with said they don't do that and my choices were to just get extra towels or get a full cleaning. They also were confused about what day the included trash and towel service would take place. I did get extra towels and they didn't charge me for them, and it was really not a big deal. I think it is just because the DVC portion is so new, they are still learning and I am sure that next year when we are there they will have a better understanding of the particulars of DVC. That was a very minor "complaint" but if I had to pick something, that would be the only negative. We loved it and have already booked for 11 months from now and can't wait to go back.