However, I think speculation is more of a "gamble" then the cash flow model.

Your business is a terrific model to follow.One thing I might do differently (for myself) is accept a partial payment in some circumstances.

My own refrigerator, very basic model, will be 14 years old soon.

Again I would highly recommend getting very competent legal advice if you are working preforeclosures in California.I'm not a "the sky is falling" kind of guy, but with legislation that can even be "conservatively construed" to include my business model I would be very cautious.There's really two ways to go with it.

I can do the arithmetic to evaluate it based on the operating expense model used on this site (you are the one that created this method?).

Following the CEO model, the President has unlimited leverage.

I can also put an older model 77 decent 2 bedroom beside this one for a total cost of around 3k- sell for 6, rent for $500.

Friedman supported both Keynesian theory AND the FDR economic models until he lived long enough to see what horrid effects both have on reality's "test" on both theories.

I would like $20K a month in cash flow, what kind of initial investment would you guys think resonable for this model?

The key to becoming an investor is be able to take a sound investment model, inject it into reality and have decent chance of success.