As far as the Fox Body goes, I think you'll find yourself fixing things constantly, and you'll be lucky if you get HALF of that 37 MPG that you seem to love so much.
+1 on the fixing things constantly. any car in its mid 20s is gonna need lots of love; but foxes are a LOT easier to wrench on then the contour platform, and parts are cheaper as well.
Highest MPG ive heard from a 4 banger turbo fox is 35mpg, shifting at 2k, 65mph with a tailwind. and it was FAR from stock. a 302 is gonna be lucky to get low 20s. My 84 SVO gets a whopping 18mpg highway, but i blame my right foot and the pig rich tune ive got on the ECU currently. Once it drops below 40deg it gets parked in the garage.
not to mention the fox body is a front heavy pig, even in 4 banger form. sure is fun to go sideways in em though