Howdy gang, I really need your help on this. I'm a builder, not a legal brainiac

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In the past, I have always built my arcade boxes and sold them without any software what so ever on them, just to be safe.
However, I'm having a lot of customers ask me about including games. I have no problem buying Windoes XP OEM when I purchase all the computer hardware and installing it. Where I start to go black is MAME, and some roms.
Now, I would never charge for MAME. If I put it on the system, it would not increase the price of the box in the slightest. Is it ok to do it this way? Should I still contact MameDev about including it? I'd even be willing to send some Money MameDevs way per box sold, because I think sales would go up if mame was inlcuded, and that is only fair.
What about roms, have StarRoms been deemed legal if I purchase them on behalf of my customer? What about buying PC arcade collections like Atari Collections and Midway arcade classics. Is it legal to include that software, but use the roms out of a frontend with Mame instead?
Should I just drop it, and go back to "System is ready for OS installation" and leave it alone.
Thanks for the time guys.