Micro gravity and a vacuum are two different environments. We can create a vacuum on the surface of earth (full of gravity) or have the space station have micro gravity with no vacuum inside the station itself. The depths of space have both micro gravity and a vacuum.

Mass is certainly relevant in micro gravity. Kinetic energy (like a moving bullet) is bound to mass. More mass, more kinetic energy. So if you were to shoot a heavier bullet at the same speed as your vector, the bullet would have a higher energy. Then equal and opposite forces blah blah blah...

Your relative travel time might have been instantaneous, yes, but the universe around you experienced the relative normal flow of time. So while your trip may have been instantaneous, you've "traveled forward in time" as the universe aged while you were moving at light speed. So sure, your perspective was instant, but your resulting destination was not instant.

Umm no sorry that isn't right... light speed is not instantaneous. On a small scale (earth sizes) it could reasonably be considered instantaneous, but anything bigger, not a chance. Light takes 8 minutes to get from the sun to earth and that distance is absolutely minuscule on the galactic and cosmic scale.