(3) Is it possible to use the field/mass time differential to generate anti-gravity effects?
Assume that a quantum theory of gravity consistent with Special Relativity exists, such that the gravitational force is transmitted by gauge bosons (gravitons) moving at the speed of light. The short-lived particle mass which generates the graviton field is necessarily moving slower than light. Reference frames exist for which the graviton field continues to exist after the particle mass ceases to exist. Since the graviton field in the absence of the particle mass represents an asymmetry and a violation of the conservation of energy (?) such a reference frame should experience an offsetting change in mass, somewhere. (That at least is the idea.)
Of course, with a field of virtual particles, it gets tricky, since theoretically they already "borrow" energy by exploiting the Heisenberg uncertainty relation between energy and time.