The 80's electronics in the AFM aren't that tiny, so you should be fine. Or, grab a small breadboard + components practice. It's quite easy once you get a few hours under your belt.
Haven't heard of this AIP replacement, so can't comment.
You can get the history of it checked via sites like http://www.japanesehistorycheck.com/
or http://www.japaneseodometercheck.com/
$6,000 seems quite cheap, location? I'd have it thoroughly looked over before buying.
Well from my experience, some tyre shops can't put wheel nuts on properly, and when they do a "toe check" they mess up the alignment more than it was already, so I'm not surprised some can't tell the difference between PS4 and PS4S.