On the topic of "how much will I need" -- obviously, if you change your lifestyle by travelling more, etc., there will perhaps be a financial impact.
However, to maintain your current lifestyle, here are some things that will reduce your expenses from today's spending:
- No more commuting; perhaps one less car, cheaper insurance, etc.
- No more work clothes, less dry cleaning, etc.
- No more work lunches
- Much reduced taxable income, so much reduced taxes]
- No more savings for retirement, through 401k, Social Security, and after-tax savings
You'll have to go through your own figures, but I'll bet you'll find that your current lifestyle costs you no more than half your gross pay.