If you have a visa proof of onward travel is not required. If the airline asks for this just show them you have a valid visa and not required. Happens to me every time I come back from the U.S. The airline asks me where my return ticket is, I show them the reentry permit (visa is same for this) and I am good to go
Must be a new version of the form. I always have used the one page version from their website and they never refuse it. Do your extension first. Then do the reentry permit.
The reentry permit will only be valid until your current extension of stay ends. So get the reentry permit the same day after you get your extension of stay to get a full year if you want a multiple reentry.