NCREIF Real Estate Correlation to:Russell 3000 Index: 0.23Barclays US Aggregate: -0.24NAREIT: 0.13A correlation coefficient of 0 means that price fluctuations are not correlated at all.

HELOCs fluctuate with the interest rate so you need to forecast if you have enough funds to cover yourself in the event of hardships where the interest rate rises, rental rates drop, vacancy rates increase etc. 

If your payment after collecting one unit of rent is less than renting the equivalent unit then all is good because see item 2.  2) You get to write off the interest related to your living unit.  3) Markets fluctuate in value but San Diego historically has always risen over enough time. 

With cash you have great negotiating power, lower closing costs, higher income and the ability to withstand extreme market fluctuations.

When a tenant doesn't pay their utilities separately (which will obviously fluctuate in price depending on the season), they have less of an incentive to conserve resources and won't think twice to leave the AC running, lights and TV on, or take long showers, resulting in higher costs for you.

Each fluctuates regularly so it's really just about maintaining that balance between the three as best as you can.

Does the spread margin over the interest rate fluctuate?

Suburbs value fluctuates often with the economic conditions that none of us can control.

In the short term rents fluctuate, long term they rise due to inflation, scarcity of land, etc.One measure of property that is rarely talked about is what would this property look like as an investment if I had to lower the price to break even, would there be a demand for it? 

Invested in a income fund you could fully retire and the higher returns would level out the fluctuations in the market.