One thing you're not accounting for is inflation. I think most people would plan on 3% at the minimum, and lots of folks would plan on at least double that for their medical-related expenses. Over the 22 years you're talking about, this makes a drastic difference. Even at 3%, your living expenses double over that time frame.
You've thrown out several different numbers ($3,000, $4,000, and $1,666 ($20K/12)) which are wildly different standards of living. This tells me you don't really know what your expenses are and don't know if you'd like living at those levels of expense. If I were you I'd try to live on whatever retirement budget you are planning for for at least 6 months to get a feel for things. If you stay in the $450K home during this time, you'll have to extrapolate on some of your budget items, but it would still be a good exercise.
If you invest in anything that gives you a 10% return, be aware that modeling a 10% constant return in a spreadsheet is far different from the 10% average return that you might get in the real world. The volatility of any investment that returns 10% average over the long term - US stocks, for example - means that when the bad times hit and you're still taking your $X out of your portfolio, that amount is a larger chunk which damages your portfolio's ability to survive. FIREcalc (
FIRECalc: A different kind of retirement calculator) can give you a good idea of how your portfolio can survive. A shortcut many use here is the 4% rule, which would mean you could count on a $200k portfolio throwing off $8k per year in spendable money -- clearly a lot less than what you think you need.
Also, you mention a wife and son in your original post but your follow-up post you only refer to yourself. If your wife and son are not already 100% on board I would begin talking with them about your ideas and feelings. If they do get on board, you'll have help and support to bounce your ideas off of. If they don't, you'll need to decide which is more important (retiring early or your family) or begin working on persuading them to your point of view.
2Cor521