.- I'd probably set aside ~10% of your gross rent for maintenance/repairs (you'll want a reserve built up for those big capital expenditures that pop up)- look up property taxes for your area- get some insurance quotes to get a more accurate insurance estimate- property management typically 1 month's rent (8.33%)- Determine if you'll be paying for any utilities

One thought I have is that you account for 10% for repairs but I would also strongly suggest that you account for 10% for capital expenditures.

Dilemma: Major Capital expenditures! 

Taking this things into consideration, I believe that paying down10K for an apartment + 5K in closing costs and taxes and rent the it out, and the rent is able to pay for mortgage, insurances, capital expenditures, vacancy and maintenance costs so that the net cashflow is 0 in the first year, at the end of 20 years I would have an apartment fully paid worth 189K (taking into consideration a 2% appreciation and 2% increase in rent for inflation) that I only really paid 15K. 

. = Deal # __________ Good Deal/ Bad Deal Location: __________ 333- Message Me Property Type: __________Price: __________Acquisition: __________Loan: __________Down Payment: (20%) - __________Closing Cost – (3%) – __________Due At Closing: __________Rehab Estimate: __________After Repair Value: __________Equity: __________Income:Rent: __________Washer/ Dryer: __________Parking: __________Storage: __________Monthly Gross: __________Expenses:Mortgage: __________Gas: __________PMI: __________Garbage: $20 {Times The Number Of Units}Electricity: __________Water & Sewer:$75 {Times The Number Of Units}Taxes: __________ /12 = __________Insurance {$100} /12 = $8.34Monthly Expenses: __________Expenses:Vacancy {5-10%}- __________Repairs and Maintenance {10%} - __________Cap Ex - {Capital Expenditures} {8%} - ________Management {10%} - __________Operating Expenses: __________ {Optional} Future Assumptions: Annual Income Growth: {2%} Annual PV Growth: {2%} Annual Expenses Growth: {2%} Sales Expenses: {9%} Totals: Monthly Income: __________ Monthly Expenses: __________ Monthly Cash Flow: _________ Annual Cash Flow: __________ Total Cash Needed: __________ Cash On Cash Return: _____Monthly Cash Flow Total Including Operating Savings: __________Year Total Including Operating Savings: __________

Unless of course you are using them to fund capital expenditures or maintenance or some other qualifying expense.

As for your question, my goal is to have enough cash flowing passive income from rental properties to supplement my military retirement in 8 years without reducing my families expenditures.  

You should prepare for some capital expenditures to update utilities that are provided by the park.  

My immediate reaction is apply the most you can to the (2) units today, to mitigate future capital expenditures.

I would highly suggest in accounting for at least 10% for each property management, capital expenditures, and repairs on top of your PITI (principle, interest, taxes, and insurance) assuming that the tenant is paying all other expenses.