Not leaving the country but leaving my living situation

So, I’m asking what the best way to reduce personal items before moving from your long-term partner living quarters to downsize into your own 1LDK (or whatever I can find!) would be.

Due to my job and other personal circumstances, I’m staying in Japan but feel like I will have to move out soon.

I have a total of three DIY PC’s with four different monitors and keyboard/mouse sets to get rid of;

computer desks that I might abandon (leaving at partners) because they are too big for transport or try to sell;

I have a NAS Server that I don’t know if it’s worth taking along but probably will take, anyway;

Guitars (5) that I want to keep (but not sure about how new place will allow them);

Radio control and scale models (probably have to claim some of the shelves that are here) that actually don’t take a lot of space, but going back to living alone probably won’t have that luxury, anymore.

I bring this up because as I was telling her about how our area against the mountain is rusting my strings, her comment (possibly a Freudian slip), suggested that I move somewhere where they won’t rust…

So, now that thought in the back of my head seems to be coming to a reality and I may have to find another place within a few months.

I know that places like “Book-off” will take things, but not always at a good price.
The DIY PC may be a challenge and probably a “Book-off” item because I don’t want to haul that stuff back home and might take whatever I can get.

I also have a car that I intend to take with me (because I bought it), but I may have to sacrifice the convenience of it for a downsized version.
Some of this stuff is something that I don’t even want to ask…divorced twice and moved around several times, but in an average of five to ten years (been her for over 30).

But, other than the known places for getting rid of used things, I thought by posting here, there might be something I wasn’t aware of.

Thanks for the input.