The romulans have their own goals but essentially contribute to the borg reclamation project occurring on the cube where the XB's (ex-Borg) are having all their prostheses removed and undergo psyche work and are restored at least as much as possible to what they were before being assimilated.
Data isn't in it.
Well, kinda, kinda not. more like the 'ghost of Data' looming over everything.
I finally watched ST: Nemesis (the last TNG film before the reboot) and much of Season One, by the time you reach the end, feels like a "proper ending" to the story from that film. Which does involve Data.
So Data is kind of a "theme" in Season One driving a lot of Picard's decisions and the season helps resolve long-standing feelings of guilt he had over what happened in ST: N. It was actually pretty touching.
But dang. Lots of cameos. I think only a handful were helpful. (I thought Episode 7 was pretty on-mark, at least; and I think it makes sense for Jeri Ryan to be around. Plus she's playing the edgy disruptive influence, which the show needs.)