Just an FYI ... most people here have the philosophy that MAMEing a fully working cab is kinda like dressing a little boy up in women's clothing, and turning him gay. Or like molesting a small cuddly kitten. Or killing a baby seal ,or something equally disturbing.
So the typical suggestion would be to find an already gutted cab to do your work.
As for the other parts of your questions...
1) Linking: You're going to have a problem linking MAME games, in fact, I don't think MAME supports that (but someone else can confirm/correct this).
2) Hacking: This usually involved finding something that is already made for the PC and wiring the arcade controls into the inputs... but there are many threads on how to do this for each individual application (ex. I bought a analog joystick on ebay, broke it out, took the POTS and used them for the POT driven gas pedals for my cab)... Pretty much all hacking requires some (minor) skill with a soldering iron.
I gave this a lot of thought one time as I actually did buy a dual sit-down style cab (working) and was contemplating MAMEing it, but decided that I didn't want to mess with a working machine and I ended up selling it (for a profit of course)

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