You might consider a hybrid approach. You might have a subset of instruments that are unique and/or precious, and others that are common.
Packing things up is a pain, especially large keyboards. Overseas shipping rates can be ridiculous. And shipping is not without risks of its own. So sell off in Europe what can be easily replaced, and ship the things that are rare (with sufficient insurance and pictures to back yourself up).
Alas, most of my gear is what I'd call precious. Probably the only one I could easily sell/re-purchase is the Prophet 6 and even that is dear to me. The other things - a Juno 6 w MIDI, my ancient Pro One, a Micromoog are tricker to picture replacing. The Pro One actually flew with me from California in the fist place, in a custom suitcase. It handled the flight well enough, though it needed calibration in Berlin. I've an MS20mini that, while an easy one to replace, was a birthday gift from my ex-wife. I'm quite sentimental - that's all part of the problem!
I've got several guitars as well over there, but there's less incentive to ship those. If touring ever kicks off again, those instruments would be happy to have Berlin as home base.
Anyway, am I right in thinking that one way people ship stuff is to rent a sort of van-sized shipping container? I'm getting remarried and while my soon-to-be-wife has expressed interest in us getting our own place in Berlin, I think the pull of older parents back here means it's not gonna happen. So, I might find myself moving from Berlin altogether, packing up books, boots, CDs, LPs and such. Having all my possessions in a single container feels easier in my head than packing one box/synth/boot after the next.