I think they take an editing test and go through a series of interviews. They take a test and go through 1-2 days of interviews. Not much beyond what we must have to learn a new system. That is, there is really no training on copy desk issues. A lucky few get to go to API, Poynter etc.
Extra pages are okay.
The copy desks have made big strides in talent but still have a long way to go to earn respect from presentation and team leaders. There is not a lot of turnover here, and many of the folks who have been here a while can't get it out of their heads that the copy desk isn't worth much.