I want to have at least $250 per month that includes vacancy, repairs and capex going into an account.

Be sure to include repairs, vacancy, capex, etc. in your calculation - don't just do monthly rent minus PITI.2.

@Jarod Castaneda I have a 12 unit in a town of 16,000 with rarely a vacancy.

maybe BRRRR strategy might work better for this. also your vacancy should be between 8-10%, capex should be around 8% and the insurance seems really low for this type of house.

In our area, we could rent for more money, have more prospects, and nearly no vacancy, if it was non-age restricted.

Even though it's family, we'd have an agreement written up showing that all rental income from there goes to pay the mortgage first, then the line of credit with what remains.  4) Since it's a Heloc, if we have vacancy or maintenance issues, we could also pull additional funds from it, as we plan on getting a 200K line but only accessing 180k of it for this plan. 

My math is simple: 1) Gross Schedule Income - 7% vacancy - 50% Opex - loan payment = cash flow (I'm expecting 100 dollars per door)                              2) NOI (adjusted form realtor with the above criteria) / 8% cap rate (Florida market).     

Third, where in this calculation are you including the yearly cost for taxes, insurance, vacancy, CAPEX, etc...?

Thinking about it from the lender's perspective, it seems they would not count rental income, seeing as extended vacancy could potentially cause me to default on the loan. 

I use very conservative values (10% Capex, repairs, vacancy rates, etc) I compared it with a couple of other online calculators and it gave me similar results.