If you think about the Fire number with the FIAT Hat on, the Fire number is 25 times your annual expenses. If you a mass that amount of fiat, you supposed to be able withdrawing 4% of it and keep your life style.

There are many calculators online to help you to find your number. All of them are wrong, no ones know what would be the BTC value in the future...

So, I prefer to stack SATS as much as I can.