Changes in quantity do lead to changes in quality, but there is always a precise point where gradual quantitative changes cause a sudden qualitative change. Water remains liquid from 0C to 99C and then suddenly starts boiling at 100C. To have a proper definition of something, such a dividing point is to be found.

I meant "right amount" as in "right amount for something to be private property" and not as in "morally right".

There could be a miriad of scenarios for having 10 houses without renting them. I would love to have my own place in 10 different cities or countries so I could just go there and live without worrying about renting somewhere to stay. I could have my own little data centers in those houses and host lots of decentralised media. I could use the houses for separating my workflow: one house for my musical instruments, another for engineering etc. But whether it is a real scenario is not important. Owning 10 houses is just an example of possessing more than the majority. If it is considered to be private property, then following the same logic having a personal computer while living in an area where few people have one should also be considered to be private property and, in the case of a revolution, the computer should be seized as such. So this is not merely something hypothetical.