First, you have to accept that there is no singularities, which is more mainstream than the BigBang Theory... What i call gravity at the bigbang is the binding energy: the Unified Force.

Second, you have to accept the high probability that it was a black hole that suffer a breaking in its symmetry, not negative energy causing the expansion, simply because there was a time before time, meaning that the black hole of origin is a condensed of a past universe (no negative energy needed, just a breaking of symmetry, instability:too much matter, or a collision). This has convert a great amount of the binding energy into kinetic energy, i think half of it (see my theory).

The expansion of space is the kind of pseudo-force that makes the universe expand allegedly faster than light.

I said time on average, not time everywhere in the universe. Time dilation is due to two things, relative velocity (SR) and gravity (GR). The average timerate is proportional to the energy of the universe. The unified force of the black hole contains the entire energy of the universe. Energy is conserved, thus time on average is constant...

So the expansion of space, if there is one, is like an excess of kinetic energy or a negative energy...

The objects velocities observed are higher the farther away the objects are from us. This leads to the Dark Energy theories. But it could be simply a matter of non uniformed distribution of kinetic energy. The farther away objects are, the more kinetic energy they got from the bigbang...