an object does not possess this energy, it possesses momentum and in the event of a collision it could apply a force - for maximum force an object can apply is a function of its mass and its velocity at any given moment. Energy is an entirely abstract concept - there is no such "thing", no substance as "energy"; not at any level of existence. It is a number, a quantifier that describes how much work an object could potentially perform. This is based on mass and velocity, that is to say it is simply a mathematical outcome of momentum and a prediction of how much force could therefore be applied by collision. If an object has no mass it cannot apply force and it does not, by definition, have any energy.

no mass equals no existence, hence virtual particles do not exist, hence photons are NOT virtual particles without mass or charge. E=mc^2 just relates to the energy potential of a particle if its entire mass could be converted to energy, as you correctly state this does not mean that particle possesses this energy in the form of charge. This is where most confusion comes into play. People assume that the particle possesses this energy, this is not what the math says. It is only the potential energy the particle contains if you could convert its entire mass into energy, a big difference between converting a particle to energy and a particle containing that energy.

what is charge?
what is a magnetic field?

No more answers than what is already written in books. We not believe charge is merely a potential though, something that does not exist until it needs to exist, then suddenly becomes electrical energy. We believe it is already electrical energy moving between atoms, within and around. We think charge may be smaller particles, quanta if you will.

As for magnetic fields we have no good answer except perhaps quanta in an excited state moving around the electric field. Fields have always bothered us. We "feel" everything must be particulate in some way or their could be no communication of forces, but how do you describe something you have never detected or imaged? Yes, we sense the field, but how do we sense it? What makes a field a field? It has to be more than imaginary lines drawn on paper, it must be composed of something, but what this something is, is beyond our ability to comprehend except to fall back to the insufficient explanation of quanta.