I may send some pictures at some point-- I like our boat but the tankage and storage space is small. I was reading about katydyn water makers last night, and I might be able to install one of the Powersurvivor 40 units, but I'm not sure yet if it is worth the investment.
The watermaker question is one with which I am struggling also. I carry large tanks, but part of that is ultimately ballast. A watermaker is a very good idea on a small-tanked boat, but it is a maintenance and consumables commitment and they eat a lot of amps, meaning a rethink of alternators and/or battery banks, and, once installed, must be either used or "pickled": they can't just be used on occasion and then left for three months.
I like Cam's list, and your thinking, but would encourage the following ideas: Six months before you go, install a new starter and a new alternator. Seal the old, working ones in bags with dessicant and store in a dry place. Six months with a new alt and starter should reveal any issues, like whether you need to upgrade your belt.
If your diesel is old and has been run seldom, consider a "prophylactic overhaul" whereby the cranks, rods and journals are inspected, the bores observed for scoring, and so on. Boat diesels can die from underuse, not overuse, usually. Replace anything that looks off-spec, and sail away secure knowing that the odds of throwing a rod, etc. are very much lessened. This is also an opportunity to service engine mounts, paint the bilges and to derust and paint the engine a light colour that will show oil leaks.
Impellers can and do fail. Bring several. Consider switching your raw water pump cover to "Speed seal" or whatever that thumbscrew cover is. Consider a high-temperature alarm and a low-oil pressure alarm.
Bring engine zincs, another "consumable" that can be hard to source.
Bring at least enough hose for a complete replacement, and bring enough hose clamps (aka "jubilee clips") for two complete replacements.
Consider a beefed up fuel filtering system, as in one with its own pump to pressurize the fuel side without the engine running or one which can polish fuel BEFORE it goes to the daytank. Invest in a Baja-type filter for your deck fill to get dodgy particulates out before your tanks.
Consider a daytank, perhaps gravity fed. Rig your fuel and return lines so that the daytank contains x litres of "certified clean" fuel, even if your main tanks are filled with dirty goo.
Consider rerouting the fuel and water vent lines away from the topsides/under the gunnels to higher and drier in the boat. The first three causes of diesel death are water in the fuel, from what I've gleamed.
Consider getting rid of the spring-thing in the exhaust loop and simply run an open hose high into the cockpit or someplace where the occasional spurt of water will PROVE the pump is working and which cannot fail, sucking water back into the manifold.
Bring spare gaskets, gasket goo and gasket paper of different thicknesses. Frequently, a gasket will fail slowly, leading to a weeping pump and partial loss of pressure. To you, it looks like your diesel's running 10 degrees hotter. Look in your bilge and/or keep oil pads beneath your sump. The location of water or oil will tell you where to look for problems.
Figure if there is any method that will start your diesel with zero battery volts. Practise this method, if any, a few times.
Go over the entire engine in situ
and figure out how you would remove parts for a regasketing, say, when the engine was cold, hot or when you were in heavy weather. Picture the tools you would need and the steps it would take to do these things. Type up the procedure and put them in laminated pages in your maintenance log. You will find a reason to buy fairly esoteric tools, like right-angle screwdrivers, crow's foot wrenches or socket ends and other single-use, frustration relieving devices.
Start a maintenance log!
Get a single-volume book, like Calder's Mechanical and Electrical, that covers basic to intermediate maintenance of diesels and electrical topics. Take a basic diesel course.
Do all these things, particularly the bits about keeping your fuel free from dirt and water, and you will avoid 90% of the common dead diesel issues.
Hope this helps, Jim.