Obviously check all the normal stuff that is not brand specific, runs, drives, clutch and brakes all work, not leaking like a sieve etc. Plowing, especially commercially, is hard on a vehicle as evidenced by broken leaf spring and expect that the steering and front axle hubs and bearings could all need replaced.
Rust doesn’t look “too” bad. But the repaint could be hiding a lot of bondo. May still make a good plow truck but might not be the resto project you’re hoping for.
Contrary to what you heard, manual trans IMO, is not preferable for plowing. Fine for a long driveway or 2, and some little work, but a pain in the ___and hard on clutch for commercial work or plowing parking lots or lots of driveways.
I wouldn’t turn down a manual for plowing out my driveway but I wouldn’t even consider one that I was sitting in all day or night plowing driveways and parking lots.
Back to the truck, if it runs and drives and doesn’t appear to need major surgery or excessive work and $ AND the plow works as it should, it’s a bargain at $2500. Good working commercial grade plow setup is worth most of that money and the truck is basically free or vice versa.
However whomever is selling that probably also knows that so compare the cost to the amount of work required on it.
Also knowing that super cheap plow trucks that actually work aren’t dime a dozen.
Also yesterday was Turkey Day, so consider if you can make it operational in short order, as the best plow truck is the one that keeps your from shoveling snow this winter, not sitting in your garage on jack stands with its guts on the floor.
Good luck!