There's a one-week tryout after a candidate has passed all the previous hurdles. I came for a week-long tryout in 1992, and was hired two weeks later. Both, although training for copy editors is limited. The Post has a program called In-House University, where new skills or refresher courses are taught. We also have a newsroom-wide headline critique program.
Extra pages are okay.
It's important to keep in mind that the Post is a remarkably Balkanized institution. What I say about Metro probably has no relation to what it's like on other desks, where traditions dictate other ways of doing business. Consequently, minor errors are more likely to slip through in National than in Metro. On some, smaller desks, copy editors lay out pages. The Sunday Outlook section has no copy editors at all.