My answers are in ()
The amount of space rotation is minuscle away from the object and relatively small compared to object spin near the object. It is incorrect to think that space rotates at the same rate as the object. The galaxy surrounding the black hole did not rotate with the black hole.
(Yes, you are correct, it is minuscule, which is why I stipulated that the entire galaxy accelerated to have a measurable effect on the mass body which remained.)
To answer your original question, if the entire galaxy were to accelerate in a given direction, any object left behind at most would be dragged in the same direction- not the opposite direction.
(You are, of course, right again. The object would be dragged along in the direction of the galaxy movement, so to remain stationary it must accelerate in a direction opposite the direction of the galaxy movement.)
And to answer your question about my path. Yes. I have found what I have been looking for. I am in heaven. When I die, if ever, I will just go back to work.
(I have long considered that to be happy with where you are is the only way to be happy, and you seem to have found that. - I am happy for you - No pun intended. )
So the next question is
If the entire observable universe were to accelerate a magnitude ‘A’.
Mass ‘M’ which remained stationary must experienced an acceleration ‘A’ in an opposite direction to remain stationary to prevent it from being dragged along with the universe.
Then it could be said
If mass ‘M’ is accelerated magnitude ‘A’ and the universe remains stationary per our coordinate system.
Inertia is a response of mass ‘M’ to the apparent acceleration of the universe as mass M assumes it is stationary and the universe is accelerating according to mass ‘M’s coordinate system.
You may have to read the last paragraph a few times to get you mind around it. I did.
Then again perhaps not.