Power wise: Not much you can do besides a good tune, intake, and after cat exhaust. You can beef up the 4.0 OHV with a stroker kit and other things like that. But upgrades like that cost a lot of money.
Plow: People do use a Ranger, but as you stated, use a small plow. Also I wouldn't try to plow anything more than like 5-6" deep. Being a 5spd, or even automatic, that is going to put a lot of stress on the entire drivetrain since a Ranger suspension and drivetrain is not nearly as strong as a 1/2 ton or 3/4 ton truck. Doing small jobs will be ok since this is going to be a work truck. I would not want to use my daily driver as a plow truck.
-2011 F-150 Lariat: 5.0 "Coyote" V8, 6-spd Auto (6R80E), 3.73 ELocker. White Platinum Metallic Tri-coat.
-1992 Ford Ranger: 4.0L OHV, 5spd (M5OD-R1), 3.27 Open.