For the walk: You might try straightening the legs. As it is, he is walking with his legs bent most of the time but there are a couple of points in a typical walk cycle where the legs are straight. For example, as he is pushing off for his next step, the supporting leg (#1) would straighten out to support his weight as the other leg (#2) leaves the ground. Then as this other leg (#2) swings forward and is about to hit the ground, it usually straightens out until it hits the ground and bends.
EDIT: I was looking at ver 24 while making the above comments. I just took a look at ver 25 and see you have improved the walk. Walking on that hill definately presents a few challenges with weight.