1) As far as location, Schaumburg is not a bad idea, but your friend might want to look into the Carol Stream, Glendale Heights, Wheaton area as I can think of approx. 4 different Vietnamese/Pho shops within about a 3 mile radius of each other. Pho Saigon, Pho Hoa, Nha Y and, Luong Loi (half Chinese). For some reason, population density of their target market most likely, the shops have congregated in this area like car dealers do.
2) A very rough estimate is low to mid teens for a small spot in an average strip mall up to 3-4 g's for a larger spot in a high traffic/high visibility area.