That's how I see the numbers, and the market is variable of course.

Most HELOC are variable rate.

SFH Pros:1) More space - inside & outside2) No HOA - one less semi variable cost and no rental restrictions now or in the future (remember CC&Rs can always change!)

The two main variables I just mentioned, rent and expenses, seem to be very hard predict.  

MAYBE LENDERS, if experienced investor. current rate 1-1.5% above 5/5 ARM20 year amortization, variable rate, no balloon, 5/5 ARM is fairly common. currently in the high 4% to 5% range.

-What conditions should I add to my standard purchase and sales contract to account for the variability as to whether the lender will or won't accept my short sale request?

Use HELOC for rehab funds on properties that you are planning to rehab, HELOC is variable so you don’t want to max it out and then have the rate climb and be caught with your pants down.

You have listed in there an annual net income number....that in theory would be your cash flow (assuming all of the correct variables are in there).

HMU, a lot of variables involved for your question. 

If I purchased today, I would be considering variable rate loans or loans fixed for a very short duration and then adjustable.I am likely sitting the sidelines for a while and watching the show.