De-winterization??? If the winterization was done correctly about the only thing you would need to do to be ready to ride is put in the battery (which would have been on a charger), and go ride.
I don't recommend replacing the spark plugs until you have run the engine at least once in the spring to clear out all the fogging oil, etc., that could foul a new plug. Some people recommend waiting until the spring to lube the cables, but if you use a good product and keep the ski covered you can do all that as part of the winterization process, so there is very little to do when you are ready to ride in the spring.
My local shop wanted $250 for the winterization, which included an oil change. I did it myself in about an hour for much less. See this thread:
Tips for those winterizing soon (yamaha) - PWCToday