Does energy is associated with intrinsic inertia, the rest mass?

We could have the object-at rest-annihilate with an "anti-object", producing radiation possessing energy. so, yes there is energy associated with the rest mass.

While creating object, various particles like electrons, protons, neutrons are to be brought in together. Every bit of energy that goes into creating the object would be accompanied by an increment in inertia according to relation E = mC2

The attribute energy is always accompanied by attribute inertia.

In 1905, Einstein summarized his theoretical disclovery with the sentence,

" The mass i.e. inertia of a body is a measure of its energy content."

Energy in all forms has property of inertia, the reluctance to undergo a change in velocity. The more energy that went into forming a body, the more inertia the body has.

What is Equal Apriori Probability?

A fundamental postulate of statistical mechanics is that a macroscopic system in equilibrium is equally likely to be in any of its accessible microscopic states satisfying macroscopic conditions of system. It is called the postulate of equal apriori probability.

According to this postulate, the probability of finding the phase point for given system in any region of phase space is identical with that for any other region of equal extension or volume. This may also be stated as for a system in equilibrium, all accessible microstates corresponding to a given microstate are equally probable.

The basis for the postulate of Equal Apriori Probability is ergodic hypothesis. The constancy of volume element in phase space with time indicate validity of postulate of Equal Apriori Probability.