you don't need to chop it to read it. but read all four. each cylinder is different. one could be fouled, the carburators could be out of sync. a jet may be clogged. etc. you want consistency on the reads as well as a proper ratio for each cylinder.
yes but the thing about plug chopping is that you are actually supposed to kill the engine while pulling in the clutch at the same time so the plug being chopped isn't "blown clean" by the next compression stroke
about impossible to do on a multi..........
pretty much a procedure for singles and twins has been my experience