I need to replace my right rear OEM Continental tire due to a nail in the shoulder. According to several sources this means the tire must be replaced.

This tire is on national back order for what is most likely months.

So, now I'm looking at the Goodyear Eagle F1 All Season and the Yokohama ADVAN S.4.

If I get one of these, should I replace one, two or all four tires?
I am on a limited budget, but from what I've read both of these are superior to the Continental. Perhaps I can replace both rears, and then do the fronts in a couple of months?

I do want all season tires as my Xfire is a year round car.

Thanks in advance for any advice on this.