NCountry...good topic. We started out hoping for a 5% ROI to keep us going and afloat on what we thought was a pretty liberal budget, but over the last 5 years both the % and the budget difficult to achieve. Now, of course you can get 5% due to rising inflation and interest rates but 10% may prove elusive over the long term as there tends to be a lot more volatility as you increase your risk.
2. Cutting down and simplifying your lifestyle now can certainly help extend your cruising life but I wouldn't expect 5 years of luxury denial to get you a whole bunch of time unless you take a lot of plane trips and drive a mercedes! The way we did it mostly was to bank one salary while living off the other and trying to bank as much of that one as possible. Budgets did not even consider the second salary. We also were frugal and bought used cars and took family vacations on the boat. One of the big surprises for me was how much maintenance and repairs will cost you when you are out cruising....and in talking to fellow cruisers that seems to be a common theme. Assuming a boat in the 40' range for a family of 5...you really do need to budget at least 10% of the boat vallue (or at least $10K/year) for repairs and maintenance. Some years you will be lucky...others you won't but over the long term you'll spend it assuming the boat has normal systems and you are not trying to emulate the Pardees!
Lot's of cruising nurses in the US where work is easy to find wherever you drop the hook for a while...very difficult elsewhere to be allowed to get work.
Lastly...you'll find an internet banking connection and an ATM card will get you by just fine anywhere in the States/ Europe or the Caribe. You donn't need to carry a lot of cash or traveller's checks. The South Pacific and less developed areas might require a diferent strategy.
Good luck...I look forward to the continuing discussion.