Some questions are just designed to start trouble.
I’m not going to touch the first three imbroglios, but let me weigh in on the final one. I stand firmly on the side of one space.
Yes, I know some people will fight to the death for two. Take a look at this Yahoo questions page, in which an English teacher supports two spaces. I’m amused by the way she throws down her profession as if she were a doctor answering a question about strep throat or a certified general accountant addressing tax law. (Fortunately, she’s honest enough to report that her publisher disagreed and insisted on one space.)
Then there are the fence-sitters, who argue both sides against the middle. TypingCertification.com weighs the baby as King Solomon did and suggests slicing it in half. (In essence: Some people prefer the appearance of two spaces, it says, yet most mainstream publishers demand one.)