No one of us knows how many Bitcoin you will need to retire at that time.
Hell we don't even know if Bitcoin will be around in 20 years!
But let's assume Bitcoin will still exist and be the number one relevant coin.
Then imo you will need much less than your predicted amount of coins. A tiny fraction of that coul be enough!
Bitcoin's potential is massive in terms of value!
Satoshi himself said it will be either a huge success or it will fail!