No energy is needed to create a gravitational field. The energy released in the creation of a gravitational field is negative. Energy is always released by the creation of a gravitational field. The total energy of the universe could be zero!

If gravity causes the mass of a sphere to contract, energy is released and a new gravitational field is created between the previous position and new position of the shell. Since there was no gravitational field there before, there was no energy. The creation of a new gravitational field extracts energy from the shell, decreasing the energy contained in the new gravitational field. Therefore, the final energy created by gravitational field is negative. On a small scale this is almost trivial, but on a cosmological scale, total negative gravitational energy would be significant.

Once inflation begins, it’s eternal.

There may or may not have been a beginning to the universe.

Our universe is a pocket universe, one bubble inside numerous others (multiverse). Our Universe is much larger than the observable one.