Best way to estimate operating expenses on a rental?

[Craig S.]

I am looking very closely at my first deal on a duplex (owner occupied for 1 year). I have been looking at several duplexes and am trying to make sure I have all my numbers in a row.

What is the best way to ACCURATELY estimate the operating expenses for a property? I have used the 50% rule, but I want to get more specific as I am considering pulling the trigger on this deal and I want to make sure I am not underestimating or overestimating expenses.

Obviously, taxes, insurance, utilities, and vacancy expenses are relatively easy to estimate.

I will be also managing this duplex myself--should I still factor in the average 5% to 10% for management fees when looking at cashflow or because I am managing this myself should I LEAVE OUT management fees?

Maintenance, repairs, legal costs, and CapEx are more difficult to estimate however. What is the best way to go about estimating those types expenses?

Also, what am I leaving out/forgetting in what I mentioned above? I am doing my final deal analysis and want to make sure I have everything accounted for.

Here are all the "expenses" I am aware of that I need to find exact figures for:

Monthly Insurance
PMI Insurance
Mortgage Insurance
Landlord Insurance
Hazard Insurance

Monthly Property Taxes

Monthly HOA Fees (If Applicable)

Monthly Management
Management Allowance 8% of Gross Rents

Monthly Utilities (If Owner Paid)
Electric
Water
Gas
Garbage Pickup

Other Costs (Averaged Monthly)
Vacancy (7% of Gross Rents)
Advertising
Snow Removal
Landscaping
Maintenance
Office Supplies
Legal Fees
Evictions & Court Costs

Capital Expenses (Averaged Monthy)
Roofing
Furnace
A/C
Windows
Siding

Again my questions are:
1) How do I accurately estimate my maintenance & repair costs?
2) What is the best way to estimate, and how much to set aside for CapEx?
3) If I plan to manage myself, should I still factor in "management expense" of about 7% in my calculations, or can I just assume a higher cashflow?
4) How should I estimate for legal fees, court costs, advertising, etc?