What is LED1/A13? (addressing pins via variables)

can a pin have multiple watches set?

Yes, you just use setWatch multiple times on the same pin and it works fine. You can even have different levels of debounce on each watch.

How can I check 'how full' the FIFO is

I'm afraid you can't. You can however use E.getErrorFlags() to see if the FIFO has got so full that data has been dropped.

Syntax highlighting - that only happens online, and not on the Web IDE? For some reason the forum software thinks it is a reserved word :)