Everyone gets $10k. Obviously not everyone is going to pay $10k in taxes otherwise the system would be pointless and we could instead just eliminate taxes altogether. Those at the bottom would benefit, those at the top would pay more in taxes, and somewhere between is a break even point.

There's only a limited amount of stuff at any one time. Rarity and usage can make its worth different than other things. So it makes sense to track these things. Ideally, recycling allows recoup of most or all the material, which returning should provide the credits back.

It really then matters how much credits people get and thus how much resources and where. But then again, socialism and communism never talked about personal effects - but instead it talked of the machinery to create.

What the UBI enables is a migration that everyone gets the spoils of the machines of creation. The Story of Manna by Marshall Brain discusses more of how this might be possible.