My house and garden can be a place of production (for art, artisan goods, handicraft, foods, etc.).

That is not "letting the owner live off other people's labor" it's letting the owner live off their own labor. Do other people have to come over to your house and garden to make things? They should have their own house and garden. If they then want to come over to hang out and make crafts, then what would possibly be the problem?

May a musician own musical instruments or must he collect them from the warehouse of the local musical collective?

Again, so long as a type of tool is accessible to anyone, there's no issue with someone owning their own set. Whether it's a musician with an instrument or a plumber or a mechanic that owns their own tools, there's not really a problem. Nobody's going around confiscating everyone's wrenches for some ideological reason.

Suppose there's some very expensive instrument, say a massive pipe organ in some church. If that organ is not being used for profit, then it doesn't matter, but if it is being used that way, then perhaps it would make sense if various musical groups were allowed to use it occasionally, since it might not be practical to ensure everyone has their own pipe organ.

Computers and other electronics are classical dual-use goods. Do I have to share them with all kinds of people?

In a modern economy where everyone has their own computer, that's completely unnecessary. Suppose there's some remote village somewhere where they only have one computer. In that case, surely it makes sense for access to be shared.

Cars and other vehicles.

Repeating myself a lot here. Socialists aim to make transportation accessible to everyone, which generally means investing in public transit. But there are cases where it might make more sense to make it easier for everyone to have a car, like a remote region where public transportation is less viable, or a situation where people already own cars. I think most socialists would favor a gradual phasing out of cars in favor of public transit for efficiency, accessibility, and environmental reasons. A socialist state that doesn't already have cars probably wouldn't prioritize them, but that depends on the material conditions (as I said about rural regions).