Sounds like a similar setup to what we have. It's a two part machine: scanner and roll feed plotter (glorified inkjet really). I think ours only prints as wide as 36" though, not 48" like yours, so I wouldn't be able to reprint at work (hello Kinko's!).
I'm not sure about the format, but raster should be fine since I'm only going to use the scans for reprints. And I'll definitely be checking all the settings to make sure it scans at 100%. Should I need vector for some reason, I have people who could convert it for me.
I am wondering how large a file the plans will create when I scan them. They're 38" by 50" which isn't exactly small, and I intend to scan at high resolution.