2) Vacuum doesn't "suck". Take a metal big empty ball, split it into 2 semi-spheres. Join the 2 parts and remove all the air inside. You would not be able to separate the 2 pieces even with two horses.Now bring the ball outside the atmosphere. The 2 parts will fall apart without any pull. The vacuum doesn't pull. It is the atmosphere that pushes.

Besides, to move things you need energy... You can call it dark or "sucking" energy, it still remains unknown energy. Also the energy needs to be applied ("to touch") to particles.

So either you imply that this Vacuum energy only pulls on the boundaries and the other galaxies are pulled by gravity. This vision has many implications that can be falsified, like it implies that there is a center in the universe and so we should find an evident direction on the expansion, which doesn't seems the case.

Or you imply that this pull applies to every particle in the universe... Just like dark energy...

1) Modified gravity models are able to explain the movement of specific galaxies, but they fail to explain values we measure when considering big portions of the universe. There is an article of Ethan about that, which I cannot find right now.