In general; I think even 2 billion is too much. Nobody needs that much money.

At best; I think no one should be able to have more than about 500 Million. You get one house, and one car for each adult family member if you're married with non-adult kids. Adult kids don't add uncounted vehicles; they have their own limit. Anything that is seaworthy or airworthy counts as about as much "Wealth" as you initially spent on it minus a reasonable depreciation rate yearly as determined by the market, so no buying a thing and having it lose 30% of it's value the moment you drive it off the lot after buying it.

Additionally; to block too many shenanigans; wealth added by any property that is bought sticks; 3 years at minimum. This prevents people from storing too much excess in property and shell-gaming it. A company you own or have stake in cannot lend (in a long term) or gift you property in excess of 1% to 10% the wealth limit. (Depending on what the thing is). Companies may also not hold property or money in lieu of an individual personally; everything the company owns must have a global company function; and not personally benefit one or more people only. (Basically no executive-only or owner-only Jets; everyone from the tiniest manager on up should have access to it if there's a business reason for it)