Hi there, .....
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That's as far as I've gotten to date. Any advice you folks can offer would be much appreciated
Let's assume this cabinet is just for personal entertainment instead of getting into a debate about legality guys just drop the whole debate. This machine is just for fun. Not for financial gain.
back to the principal of restoring a mame cabinet for fun.
My suggestion to you would be to get a working software setup at home and then migrate it to this mame cabinet.
I'm guessing you have a windows setup. That you use regularly so get mame running in some very basic front end on your PC at home once you have mame and some Roms you'll be able to get lots of help on forums like this to get it all configured properly with a very simple front-end like MaLa.
Mame can run on anything. Just about everybody has a laptop or old beater pc in their closet that's not getting any more use. Surely your buddy can find himself an old clunker of a doner machine running any version of Windows. It'll work! If the thing turns and you can plug it into that monitor on he is good to go.
So have you ever run a mame setup on windows before? If so awesome! You know what to do... otherwise maybe the Pi is an easier route I have zero experience with retro Pi. All I know is windows when it comes to mame... if you do go windows route I wouldn't bother with fancying up the front end. If you don't have much time to invest. Just a simple list.. Save it all in a neat little directory on your C: drive then copy that directory over to buddy's cabinet in one afternoon. Let your buddy deal with sourcing any old windows computer and getting it installed in the mame cab. You can just show up. drop the software in and do the final tweaks like control configurations etc.
If I had little to no time and it wasn't in my home to work on daily that would be my own personal approach.
Hope that gives you some more ideas