Well, 4% rule would tell you around $1-2M of current USD fiat value in a “balanced portfolio”, that should give you $40-80k/year inflation adjusted forever. Now you can figure out how much btc you need in order to get that total fiat value depending on btcs price.
Discussion
I would say 2% withdrawal rate of your Bitcoin (in BTC terms not Monopoly money)
Now calculate what you want. But I’m pretty sure you quickly realize you need more