These are legitimate questions. In some ways they have analogs that have already been "solved" (perhaps not satisfactorily). Who and how determines the property tax you owe on a building or land? But I agree that these are not trivial to answer in satisfactory ways. Societies frequently have to come up with imperfect answers.
I know we can’t expect perfect solutions, but arbitrary blanket statement such as capping wealth at $1B make no sense to me.
Wealth (or money) is a proxy for power, and if the goal is to limit one’s power, I don’t see the purpose of an arbitrary dollar amount maximum that is extremely hard and probably litigious enforce to enforce.
It would be better to suggest capping the number of companies’ boards one can sit on, or limit the number of non broad market index fund investments one can have, or some other solution that directly attacks the problem of concentration of power.
