What is the heavenly realm, the higher astral plane: a thought, a physical place somewhere in the universe which is just on a different vibrational scale? Where is it located?

It is a different vibrational plane and it overlays the physical you inhabit. There are multiple dimensions. These are inter-nested and intertwined in actuality, so no one plane is that far from another. It is a kind of loop that has many layers, but the spiraling of the energies allows them to return to the origin in regular cycles of energy flow so one is never very far away from home even though the universe is vast in appearance and multiplied manyfold by the intricacies of dimensionality factored in. It is never very far from here to anywhere. This, in a sense, is a riddle and an enigma. You will come to understand this in time.