1) If you keep it under your mattress it will be much less than what I described, because every year your nest egg will shrink due to inflation, so you'll just be able to take $25k non-inflation adjusted, which is a big difference from my $25k inflation adjusted (in 60 years, $25k will be $150k at a 3% inflation). My assumption is 0% real growth, not 0% nominal growth, which is what you'd get by keeping it under the mattress.

2) The 4% rule is based on a shorter retirement interval (30 years) than what I'm looking for (60 years). Try to go on firecalc.com and look for the statistical odds of 1M giving you 50k/y for 60 years: the failure rate is higher than the success rate, and that's based on historical data.

3) Yes, my assumptions are very conservative, but I don't believe index funds will return 7% nominal over the next few decades, the world is going to face too many problems in my opinion. That being said, pretty much all I have is invested in index funds despite my opinions (mainly because I wouldn't know where else to invest it, since both cash and bonds are sure losers to inflation), so in the best case I'll be pleasantly surprised.

Again, quite possibly I'll die much younger without even enjoying any of that freedom :-)