Reminds me of an AA-1X that I saw many years ago painted similar to that. The side of the plane had a bit of nose art proclaiming it as an F4F “Hell Kitty”.
I think you summed it up about using 2″ numbers. What you might consider is leaving an area on the side where you could put 10″ temporary stick-on numbers.
Good luck with the paint job! That should be a fun project.