use the rule that leaves you in the worst case scenario. favoring one rule more than the other because it gives you more cashflow is probably a bad idea. also you just calculated your maximum asking price to meet the 1% rule....what about your rehab budget?

You might use the BP deal calculators to help you get over the hump and pull the trigger on a deal.

I see two ways to calculate my investment:1) Historical approach - the amount of the original downpayment plus renovation costs and 2) Present status - the value/equity that is tied up, but would reap if I sold it. 

It could be a bank or portfolio who finances your commercial deal, as most all will consider it separate from your residential holdings.Your debt service coverage ratio is more important and calculated property specific.

If you can't find cap rate comps  for SFR's, how would you go about calculating if a property is a good investment in that market?

I used the calculator on here and it said i would pretty much break even but I also dont know what to put in for some of the values.

If you own a property free & clear or when calculating for a cash purchase, do you still calculate a vacancy expense when determining cash flow?  

However you could finance 100K(plus any closings) which would provide the cash to pay the 20K back.Where people get in trouble is when they do the opposite - pull out cash and decrease the amount of their loans - that is called a taxable boot. 

Are you sure you can calculate the repairs/ARV without forgetting anything?  

Closing costs/agent costs should be calculated.