Lets say I want to buy bitcoins today and store them for 20 years to use a my retirement fund. Live comfortably, but don't need to buy a yacht or anything. How many do you think I would need to buy?
It's up to bitcoin price in 20 years later
But, i think 100 bitcoin is enough if bitcoin price can reach $200.000 (don't forget about inflation too)
And it's up to where you live too