Some of my suggestions:
diesel and gearbox maintenance/teardown/rebuild
Much too ambitious, WRT teardown/rebuild. You get a boat with a decent engine and learn how to maintain it properly. I.e., regular oil changes, proper fuel filters, be sure the fuel tank is clean and the fuel is clean before you start and keep it that way. You don't do an engine rebuild on a one-year or two-year cruise, and you shouldn't have to if the engine was in good condition when you started. Gearbox? If it's not right you need an expert. Pure and simple.
Minor sail repairs are no big deal. Go visit a sail loft for a couple days to get an idea of how they're sewn and laid out. Get a sail palm, good sail needles and thread, some two-sided carpet tape for the emergency repair. More important is the condition of the sails when you start out, and proper sail handling and sail trim as you are sailing. The better you treat the sails, the more prudent your sail trim, the lower the risk that you would need major repairs. In our 18 years we had few sail repairs, and the most serious was because we should have been using a storm sail, not our mainsail, in 50 knots of wind.
Again, not a big deal. You can learn quite a bit just by observing work done in a boat yard. However, be sure you're observing the pros, not some do-it-yourselfer cobbling something together. Some of the DIY guys are very, very good, but until you can tell the difference between the good and the bad, watch the pros. Accidents happen, so you are likely to need to make some repairs, but again, for minor problems in a well-found boat, you don't need magic.
This is a big issue, and one I'm not the best person to give advice on. The most expensive isn't necessarily the best (I won't go into my long rant about that, but sometime in the future, maybe). My opinion is: you find the one that is most recommended by cruisers who have used the equipment extensively. You then get that for your boat (if it's not already on the one you buy), and use it as much as possible for at least 30 days before you plan to leave. "burn in", defective units will show up problems rather quickly under most circumstances. Most of the gear on SV Watermelon lasted the entire 18 years we sailed her, except for what was fried by a lightning strike (and even some of that was repaired!)
navigation (but I can always just rely on GPS right??)
Navigation is not simply punching in waypoints on a GPS. In my opinion, this is one of the most important skills that you AND your wife need to learn. This is coastal cruising, reading charts, calculating and following a rhumb line, being able to translate and relate the 2D chart to the 3D scene you are approaching. This is something one needs to train themselves for, it is not intuitive.
"staying happily married at sea" course https://www.cruiserlog.com/forums/pub...R#>/tongue.gif
You wife needs to learn to sail as well. She needs to have her own voice and you have to know how to listen to her. There should not be rigid gender roles on board (but some jobs are "pink" because I like doing them, some jobs are "blue" because Peter is better at them and doesn't mind doing them, and we have friends whose blue and pink jobs are the opposite of ours). And you can't yell at her.
seamanship skillls (e.g. never had to cope with seaway, big current, Cape Horn type storm)
I don't think that any sailor has encountered even a significant number of difficult or problematical sailing conditions before setting out on their first two dozen passage. What is important is a well-found boat, a knowledge of sail trim, an understanding of weather in general and how your boat behaves in various weather situations. Good navigation skills - how close to land you are, how fast you will move, etc. And calm.
planning a passage, dealing with authorties
Planning a passage isn't so terrible, but remember, if your boat averages 6 knots, plan on a 5 knot passage. And add 12 hours in case you arrive just at sunset. Dealing with authorities isn't a big deal, so long as you (a) dress conservatively (no bathing suits, running shorts, bare chests or raggy t-shirts; (https://www.cruiserlog.com/forums/pub...DIR#>/cool.gif
recognize that they are the boss, and you must complete forms exactly as they wish; © smile. And bring a book or magazine with you so you don't get annoyed when they take their time. In fact, you do the last and you will often be the first one to be cleared, and quickly. It is the rare official that sets out to make your life miserable, though there are a lot of unknowledgeable ones, and you can't argue with them. But rarely did we encounter any problems at all - the worst were those who were looking for a little bit of "baksheesh" (cash gift). I don't think that we encountered it more than two or three times, and only once did we feel the need to make a little "contribution" to an official's ** fund. Not the issue you're worried about as long as you observe the law.
provisioning, cooking at sea
Practice. You've got plenty of time. It isn't rocket science. Your first forays are going to be coastal, probably weekend trips, and that's when you'll learn.
equipment and safety
Read through here, read lots more, and ask questions of us. You should take your time learning about this.
OMG... this list is getting crazy already!
Do you think we need to do a few ocean passages prior to setting off for a year?
How did you learn to drive a car? Buy a car and immediately get in it and drive cross-country? Yes, I think you need to sail as much as possible on weekends, a vacation or two, before thinking of setting out. And a few ocean passages as crew on somebody else's boat will help you get an idea of how things are done, right and wrong ways.
Finally, you aren't even going to get halfway around the world in a year. Those we met who took a one- or two-year sabbatical succeeded in getting from California to Australia. To expect to get further is unrealistic or working 'way too hard for it to be fun.
Pretty much how we did it.