Routine maintenance is generally not too difficult. Having the right tooling helps a lot.
1. Oil changes aren't too bad. Get an oil change suction tank to suck oil up the dipstick tube. Hopefully you have a remote-mounted filter.
2. Spark plugs are like a car.
3. The outdrive should be pulled every year, or at least every other year. The u-joints and gimbal bearing should be checked and greased, if possible. Check alignment with an alignment tool. These can be bought or made. An outdrive jack or stand will make all the difference wrestling with the drive. These can be bought or made. Even a wooden stand works. There should be a few youtube videos on pulling the drive and re-installing. Its not a bad job unless things have already gone bad inside.
4. Winterizing, if applcable, is covered in the manuals. Either drain any fresh water cooling and plumbing systems, or replace the water with antifreeze.
5. Like others, I'd like to have a diagnostic scanner, but I really haven't needed it yet. I know, I'll need it sometime and not have one......
For tooling you might look at:
http://forums.iboats.com/forum/engine-r ... -outdrives Look at the first two "Closed, Sticky" items. These have tooling info and several "How To" threads.