I have some vague idea about #1, but I'm not certain myself. I'd have to look at some sources to tell, and that's kinda cheating.
We've already dropped a big hint about #2--it's a one-off car.
I'm not sure about #3, though if "badge engineering" is counted, I know of at least one.
#4 has lots of answers, depending on who you count as the designer of the original 914 shape. There is considerable debate about exactly who did that.
The answer to #5 has been posted on this BBS, but it was a couple of years ago or more. The phrase "Rorty little runner" was applied to the particular experiment.
--DD