The best portable solution for the rear nuts is a Craftsman stubby 15mm combo wrench from Sears. Its half the length of a traditional wrench, cheap, fairly light and very effective. The bike specific wrenches I have seen are either very expensive, or cheap pedal wrenches that are not up to the task.
Also I doubt you will be able to fit any studded tire on the 925 with fenders. You maybe able to fit the studded tires without the fenders. I like the long-reach caliper brakes on the bike but they don't have quite as much clearance as a canti.
Craig

Congrats on your new ride.