Your year begins on the date of your first OWE travel, not when the ticket was purchased.

So far as the OWE trip is concerned it's perfectly okay to fly home from an intermediate point on a separate ticket, then return later to continue the journey.

Sure, you can re-issue to drop a segment. When the intermediate segment is "enroute" to my further destination I've also had them collect both coupons at check-in rather than re-issue. I don't know if I got lucky or this is a matter of course.