Now let's consider the gasses expand so much and such that the gravitational energy is significant and they stay together with no expansion and galaxies are formed. At that point, the gasses have no inertia energy or entropy to further expand.

Unlike most who believed that entropy would go up, at that point entropy can no longer go up but rather stay unchanged or even decrease with a shrinking space. I.e. our universe will not have an entropy death.

Thus, the entropy of molecules or the energy needed to create the vacuum at the beginning of the expansion is from the stored gravitational potential energy between molecules and not a mysterious energy form.

Inertia simply represents the capability of mass to store kinetic energy.

Wolfgang Konle ,

You said, "Inertia simply represents the capability of mass to store kinetic energy."

I agree with you.

I am comparing two objects with same mass and same kinetic energy that stay inert for different period of time, i.e., comparing the energy needed before it gains its kinetic energy to create such an environment for it.

Origin of entropy is now speculated in this preprint:

Preprint A Thought on the Origin and Limit of Entropy