It appears you've got plenty of time to sort things out. And, lots of resouces here to network with in the meantime, as well. Great suggestions and empathy from lots of folks with the same dreams & nightmares.
Bruce and I are building our own boat to be our future home, and have the benefit of having done short runs of cruising (1 to 2 months out at a time) so we have a better feel for what we want and need.
Regarding the process of "shedding" -- as others have already said, ask yourself can this be useful/fit on my boat? There are some great books out there on just this subject. PM me and I'll be happy to give you a couple of names of the books we've read.
As you go through the process of shedding, make your purchase/cleaning house decision based on that principle. I determined I need one set of items for the boat and another for the land-based home (we may not be successful in selling our house in 2 or 3 years, so I may resort to renting it out semi-furnished as an option).
Along this same line
of thought, you may want to consider long-term storage. I have some things (heirlooms and artwork I've collected over the years) that I'm NOT willing to sell/giveaway/toss. And Bruce has some expensive machine tools he's keeping. So we've decided to purchase a shipping container and put most of this sort of stuff in it and a friend who has a farm is allowing us to store it there. Other things, like the family heirlooms I'll be asking my family members to 'hold onto' for safe-keeping.
We know we most likely won't physically be able to stay out there forever, and when and if we decide times up, we'll find some remote property and build a small cabin (off the grid is our preference) and move our stuff into it. Planning for that day is a separate kitty.
I've also got a fairly detailed letter of instruction about where all this stuff is, and what to do with it in case something happens to us/me out there (probably a topic for some other thread).
Light At the End of the Tunnel:
I have 2 kids (adopted my late husband's children when they were preteens), a son 29 that I'm not on speaking terms, and a daughter 27 who is married with 2 kids (grandkids ages 9 & 6) and I get along with just fine. My significant other, Bruce has 4 great kids (2 girls 16, 17, and 2 boys 23 & 29). Most of the time they want to come with us (vacations), and this may very well be the case with you and/or perhaps your grandkids can, too.
When my kids were in the terrible teens (and also have gone through and are currently going thru again with Bruce's), my sister shared this with me and it helped so I'll share it with you.
me.Children are like dogs-loyal and affectionate
Keep positive, and as others have also said... its worth it!