Re: What did I get myself into
15 years?? That's long enough that if it wasn't fogged before it was shut down, there's a good chance it's locked up.
Remove the outdrive. Inspect gimbal bearing, u-joints, etc. Make sure it turns and shifts, re-install. Check fluid level.
Take all the spark plugs out, squirt liberal amounts of oil into the cylinders. Turn the engine over by hand a few times, make sure it's not stuck. If it's not, I'd put in fresh oil and spin the oil pump with a drill.
Check all hoses for leaks or cracking. Pour fuel down the carb, hope for the best, hit the key.
Then the maintenance stuff starts. Fuel filter, carb rebuild, etc etc.