I would say that $4M would be enough. That gives you the ability to invest the lump sum in a number or high interest savings accounts or guaranteed interest bonds. Under a relatively stable economy, you'd earn well over $100,000 a year on interest alone. Probably closer to $200,000, once you got it all invested and had a well staggered maturity schedule. (if you don't know what any of that means, you should really learn about long-term investment at your bank - it's friggin' cool).
In just a few years, once you really had your money working for you, you would have no trouble purchasing a really great house wherever you wanted and carry the mortgage with ease. Also, you wouldn't HAVE to work. I would write, or save a bit and launch a business.