These questions do indeed make sense, but they assume things about the
universe that happen to be at odds with our best current knowledge of
it.
1. There wasn't any special center point. Starting with any point, everything else moved away. There is no edge. Either the pattern goes on forever or it wraps around. On the large scale, the density at some particular age of the universe (in local standard time) is uniform
2. All forms of energy, including ones that we call mass, have the same effect on gravity.
3. There is no edge and no special center.
Mike W.
(published on 02/03/2013)