Since gravity separates very early, and takes it's present form by 1 Plank time, does it act on the energy in the very early universe (e.g., during the Grand Unification Epoch) as it does on electromagnetic energy later on? Is there analogy of wave particle duality with the force(s) in the very early universe, even though matter does not exist until the Electroweak symmetry breaking?
You are making some (not unreasonable) assumptions about the early universe that are not supported by any evidence. For example, we’re not sure that gravity was once unified with other forces and separated from them around one Planck time, although that seems plausible or likely to many physicists.
But yes, in General Relativity gravity acts on any kind of energy. (And also on momentum.) You don’t need to have mass, either to produce gravity or for gravity to act on. In the very early universe, mass was probably non-existent, although again we don’t have good evidence that this was the case. And if, for some reason, it was not non-existent, it would have been irrelevant because mass-energy would have been insignificant compared to other forms of energy.