They’d better complex it up. There’d be no point to have 1/4 of all your levels be ‘engineering sector’ in a big bunch. Ideally that would be spread out. If my last name was Erso, I’d probably split the sphere radially into more or less functionally equivalent sectors like an orange, then each of those split into the northern and southern halves that again are mostly redundant and identical. In that way, make it so each sector is fairly locally self-sufficient from an engineering, life-support, and resources standpoint. Each sector might get certain macroscale incursions from systems like the lolhuegmegaturbosuperlaser or what-not. Overall it seems to me that since said laser is not taking up a significant portion of the station’s interior volume and they do have this crazy amount of habitable volume, they must be using it for its living space potential and thus you’d expect a good portion of that volume to be for troopers to live, eat, socialize, exercise, etc. Lots of gyms, mess halls, entertainment facilities, lots of laundry, banks, etc. While it obviously doesn’t fit the Empire’s aesthetic, I figure there’s gotta be some gardens going on in there, at least some kind of food generation and processing arrangement.
We have seen trash compacting, detention centers, hanger bays, some of the command and control; but the brief glimpse from the movie doesn’t answer the hard questions like “could the Max Rebo band book a tour on the Death Star cantina circuit?”