My sister, who lives in midtown Manhattan, lives in an apartment smaller than this place. If you're downsizing from a bigger place, you basically get rid of everything. I have 30+ wine glasses in my condo in Chicago. My sister has two.
The other thing that happens in a tiny space: you end up buying quality. You will wait to find "just the right desk lamp" and then pay a premium for it.
I've got 30 lineal feet of bookshelves in my house that are filled with books I bought over the last 30 years. If I lived in my sister's house, I'd have to get rid of 80% of them.
Books are the one thing that a subgroup of hackers has a hard time parting with. I'm fairly minimalistic with all of my possessions, but books... man, I would have a really hard time getting rid of my library :(
I'm a lot more pragmatic. If Amazon told me they would give me an ebook version of each book I sent to them, I would immediately get rid of 90% of my books (everything except my coffee table books and a couple dozen books that hold sentimental value.)
Nope, no minimum room size for single-room occupancy. Minimum square footage in NYC for 2 people is around 140 square feet I believe. I lived in a 6'x10' space on east 82nd street for years, and paid a fourth what my neighbors paid in rent. Of course that was still more than I pay now for my 2BR in Seattle...
The other thing that happens in a tiny space: you end up buying quality. You will wait to find "just the right desk lamp" and then pay a premium for it.