I sold everything. Three regrets, and the pattern in them is the useful part.
A good chef's knife and a cast iron pan. Not expensive to replace but the replacements are not the same — those two were properly worn in. Anything that improves with use is a bad thing to sell.
Photographs and papers I thought were digitised and were not. This is the only irreplaceable category and I nearly lost it by not checking. Whatever else you do, go through the paper before it goes anywhere.
A desk chair I had spent a long time choosing. Replacing it meant repeating the research and the money, and I got a worse one.
What I did not regret at all: furniture, kitchen equipment, books, clothes, electronics. All of it was replaceable, most of it more cheaply than storing it, and a surprising amount I never thought about again.
The rule I would give someone at your point: sell the replaceable, keep the irreplaceable and the worn-in, and be ruthless about which is which. The list of genuinely irreplaceable things is short — usually documents, photographs, a few sentimental objects and any tool you have shaped to yourself. That fits in a corner, not a unit.