I think you need to really nail down what kind of experience and output you’re trying to create for your audience. Like if you need a top down black and white line drawing of the school to print out, Unreal is probably not the best choice.
If you want a 3D mockup of the school to add some visual flare to the 2D map, sure you could use Unreal, but maybe there’s 3D software you’re much more familiar with that could get it done faster for you.
If you want a fully explorable 3d environment where students and parents walk around virtually like a game, you should ask yourself if that’s really the most useful thing. And how are people going to consume this 3d experience? You’re also referencing Google Maps, so do you need to program GPS directions or other interactivity?
RealityScan is an easy way to do photogrammetry, but I don’t expect it will work very well on such a massive physical area, and you are limited to a few hundred photos at a time. RealityCapture has the power to recreate every inch of the school but like you said you need to provide it a ton of data.
One thing you could also consider is Twinmotion. Similar PC specs required for Unreal Engine, but it’s much easier to learn and put together environments. You can output stills, video, .exe, and 360 panoramas. If you’re paying for a full license you can also host those panoramas on our website for a virtual tour.
I will do a shameless plug here and point you to this presentation I did giving an overview of these products. Maybe that gives you some more ideas around the complexity involved in any of these approaches.