It wouldn't hurt to:
change the gear oil in the lower unit
if the impeller was done within a year of laying it up you might be ok to do a "test start". Otherwise it may be worth changing - rubber dry rots from sitting and if you live in area that sees drastic temperature changes (snow/-20 winter - 90 degree summers) that can expedite the deterioration - if you opt not to do the impeller, pay close attention when you do fire it up to make sure she is pumping water (I would do this in a barrel or with a motor flusher, not on the water where you may need a tow back)
pull the spark plugs and have a look - for the cost, new ones wouldn't hurt
have a good look "under the hood" at all the wiring, hoses, tubes etc - make sure a mouse or something didn't set up shop and have a munch
Was the motor prepped at all for storage? stabilized gas ran through it before it was left? plugs pulled and a shot or two of engine fog sprayed in?
If not, before trying to start, I would give the cylinders a shot - fogging oil is best, but even WD40 would be better than nothing (can do this when you pull the plugs to check them) - then with the plugs still out, just rotate the flywheel by hand for a couple of rotations - just to make sure nothing is "froze up" and to get a bit of oil on the cylinder walls.
Once you are happy with everything, with new gas/oil I would either 1) put in the sufficient amount of SeaFoam (added to the gas) and run the motor for a bit (again in a pail/tank or flusher) OR 2) grab a can of PowerTune (Merc product) or Ring Free (Yami product) and just follow the instructions on the can. Any of those products will clean out any "residual cooties" from it sitting around.
