The part with the 4 giant arms, if that's what they're called, looks to be some type of docking station that can move when the ship is docked with it. When the ship part leaves to go wherever, the docking station remains. It will be a hub and the ship part might have smaller ships, maybe the size of the SR1, that are sent to different parts of Andromeda to explore and the main character might be in charge of one of those ships. Just a guess on my part.
The central, spherical region is also reminiscent of a Quarian liveship to me, and I suspect it is probably the Bernal Sphere-esque concept art that they showed us awhile ago. The ring around it looks like a Stanford torus, like the Presidium was. The ship has a very interesting design. I'm not so sure I agree that the central part is mobile like you think, solely because I suspect the central part is a massive living environment, but it would be interesting if part of the ship is stationary and part is mobile.