I'm not a FIRE aspirant but I do make my living through financial markets. So I have a few comments that will affect you after you reach whatever your trigger number is:
- Think about your and your spouse's life expectancy. If, say, you want to stop earning salaries at age 35, you could very well need your money to last 50 years or more.
- Stock market returns are lumpy. In other words, the annual return of 6%-8% you often hear about is an average. Your asset allocation and strategy need to be able to withstand big, potentially multi-year dips.
- If you live in the US, be sure to factor in how much health insurance will cost you. Individual insurance (as opposed to insurance obtained through an employer) is very, very expensive for relatively minimal coverage.
- When you rely on investments for income, you have to approach tax planning and payments much differently than when you're a salaried worker.
- If you don't know much about personal finance, economics, and finance, you will either have to learn or pay advisors. Advisors' fees can be expensive both in the short term and, especially, over time.
- Families with high levels of assets will not receive much financial aid from colleges and universities.
All excellent points especially the oft overlooked medical insurance.
One other I would suggest considering is the location one chooses to live and its cost of living ratio. Living in Honolulu Hawaii or Pacific heights in San Francisco is a sizable difference to exurb of middle sized town USA.
A low cost of living area without a mortgage? The amount needed to live relatively well is a much more comfortable target. And it means one's income can be kept at a more....bureaucratic cooperative way