1. Violating the Mame license is really your last worry in the world when it comes to selling game cabinets. The Mame license isn't a law, didn't exist at all for about the first 25 releases and would neither stand up in court, nor be defended in court. Mame itself couldn't be developed in a 100 percent legal manner, since it has specific support for bootleg romsets and variants, something that is impossible to develop legally because technically there is no legal way to do so.
2. The mamedev website seems to have added a bit to the wording on the release of some roms. Jamie Fenton straight up posted on her website that "As the rights to this game have reverted to me, I have chosen to permit MAME users to duplicate and play the ROM images for Robby Roto free of charge." She didn't say non-commercial use, or set any restrictions whatsoever, and it wouldn't surprise me if some of the other releases were more open as well.
3-6. Yep.
7. Which still seems to be almost nothing these days. Amazon.com sells multiboards. You can buy 60 in 1 machines from basically every pinball, jukebox, arcade and pool table vendor in the country.
8-10 Yep, although the licenses of PC software rarely stand up in court when challenged.
11. See #7. Might also add the issue of, how do we actually know the multiboards are illegal. Of course we all know they are. But they aren't presented as an illegal product. I can buy them on Amazon.com and from 100 other legitimate vendors. I can walk into Amini's huge showroom in St. Louis right now and buy a brand new 60 in 1 right off the showroom floor, pay sales tax on it and they will pay taxes on their profit. The 60 in 1 is probably the world's most common arcade game at this point, and it is powered by mame and it seems no one involved is bothering to defend their copyrights at all.
12. Yep.
Here are the facts for USA:
1) you can't include MAME with anything you sell.
2) there are about 3 public domain ROM's that you can include with a sale... but see fact #1.
3) adding them for "free" is the same as charging for them.
4) pointing a customer to where they can "obtain" ROM's is the same as including/charging for them.
5) there is no "gray area".
6) the chances of being sued/arrested for a cabinet with 99,999 games that you made and keep in your house are virtually zero.
7) sale and/or display of the above cabinet increases your risk.
8 ) people have been prosecuted.
9) people have avoided prosecution.
10) some PC collections forbid resale, which is what you would be doing by including them.
11) multi-game boards are generally illegal.
12) artwork/characters are not public domain.
13) opinion, ethics and/or past experiences do not change the above facts.