How about take (in no order):
1. 1 or 2 fancy cars/suvs
2. Be able to travel business class (say once a month) for vacations and stay in decent hotels
3. Nice education (say 2 degrees at a top college)
4. Nice house (say 2 rooms per family member in a "decent" neighborhood) (add things like backyard, poop etc if you like)
5. Obviously enough money to pay taxes
6. Oh and ensure health-issue-free lifestyle
7. (Hobby or two)
8. (Ultra Branded clothing?)
See what it takes to get all of the above and double it. Or even 3x it. Ymmv ofcourse. I am not a traveller so fancy hotels or biz class is not a big deal. I am also not a car person so 1 and 2 are not big deals for now (things can always change).
I still can't see this needing billionaire status?
What if I have 10 ideas that require that?
Add a buffer for risk and uncertainty about the future.
And then consider what role location has on the whole package. If you want proximity to one of the global hubs / power centers, then you're looking at doing this all in a top-tier cost market.
Then you easily push into tens of millions. Breaking a hundred million to super thoroughly check those boxes isn't a stretch.
This is before considering an agenda / passion that you want to see changed in the world. And before any ambitious desires from family members and close friends.
What would be the penalty for an asshole like me having three hobbies instead of the two allowed under your plan?
Am I allowed to have one flute, or if I play professionally am I allowed to have two in case one is broken? Am I allowed to have an alto flute and a bass flute as well, or am I limited to just the garden-variety soprano flute?
I feel like there must be some way these two problems can help solve eachother.
Do you think restricting the amount of money people can make and therefore pay taxes on is a good way to pay for universal basic income? Elon Musk will famously pay something like $12 billion this year. What’s the best way to sustain welfare programs that you like without a large tax base?
the most fair approach is probably starting with "how little money should people be allowed to have" (UBI) and then what ever is leftover is fair game.
Republics are a type of democracy.