I would check out Recallbox. It's quite polished feeling and looking. It can run on a raspberry pi, or something more powerful. You mention accessing the files and I liked the SMB access because I could just cut and paste my new ROMs over from the PC or phone. I imagine you could set up a script to do this automatically or just expose a read only SMB server for your friends to access. If your games are older, like Atari or Sega Genesis this would work great. If you have big ROMs like Gamecube or Xbox, then you'll probably need a different solution since copying entire romsets to the device itself may not be practical.
I have seen a DIY Steam-ish software floating around, hopefully someone pitches in to get you that link as well.
I hope your project goes well!