I purchased a triplex in Arlington Heights/Mid-City in December and the property is cash flow positive at 20% down ($7797 gross rents - $6668 PITI = $1129 net).

The math on the property is similar for me; I shoot for ~$200 cash flow and >10% IRR which should be achievable as long as there aren't any gross issues.

The gross rent rolls from the three properties is a little more than $2500 a month. 

Your Gross is about 300k shy and if it’s true the expenses are that low, this place is run like a SUPER well oiled machine.

I have an applicant who has a good credit score in mid-700s and has pay stubs grossing a little over 3 times the rent. 

To determine cash flow I always subtract the following from my Gross monthly income: Insurance, vacancy, maintenance, mortgage, management, taxes, utilities, capex.  

Property managers typically charge between 8-10% of your gross rent, so if your property rents for $500 a month (low, just a nice round number) and your PM charges 10%, you will pay them $600 a year, which really isn't much for the service they provide.

Based off the numbers you gave he's grossing $38,480 in rents a year and paying roughly $10,800 in utilities.

I was thinking along the lines of keeping 4 months of gross rents as reserves at all times and a goal of getting my portfolio to 65% debt to purchase price.

(small single family homes can easily gross $75-150k after renovations).