How much cashflow is "enough"?

[Leo R.]

I'm interested to hear how much cashflow investors think is "adequate"--given various other relevant factors (such as the number and grade of their properties, the equity/leverage position, the total valuation of the portfolio, typical annual appreciation in property value and rent, the cash reserves, etc.). 

(When I say "cashflow", I mean the average monthly net across the entire portfolio after mortgages/debt services, taxes, insurance, CapEx, vacancy, and all other expenses are deducted).

For the sake of simplicity, let's assume that the investor has NO other sources of income other than their rentals (they don't have a W2 job or anything).

Obviously, how much cashflow is "adequate" depends on an investor's unique situation (for instance, $5,000/month cashflow might be great for a person with one rental, but it might be totally insufficient for someone with 500 units....similarly, $1,000/month cashflow might be great if all you've invested is $5k, but $1,000/month cashflow would probably be terrible if you've invested 10 million).

So, what cashflow do you consider "adequate" given other relevant factors?

...interested to get folks' perspectives on this!