There are quite a few, all in the buttons and misc folders. Best bet is to download a 3.6 style, and see what's missing. Chances are, you'll have to revert a few templates as well, to get them to work on your 3.7 board.
Yes they will. template reverting will take care of the security tokens.
I've designed a number of 3.6 styles and put them on 3.7 boards. Reverting templates and adding the missing images takes care of it.
However if you have a heavily modified board, I wouldn't recommend it.
Yes but most templates have modifications to them to make them different... the question was simple so I gave a simple answer... 3.6 templates are very different then 3.7 and should not be used with modifications.