Possible 4 Plex purchase. What info am I missing?

[Russell Fugitt]

I have a few SFR's that I have successfully rented out for years. I am considering buying a 4 Plex near me and am hoping someone with more experience will look over my numbers and comment on it.

4 Units all 2 Bed 1 Bath

600/Month Per Bedroom

28800 Gross Rent

2880  Vacancy 10%

2590 Management 10% (I'll plan on managing myself, but want to put the number in)

2600 Water/Sewer/Trash (Water is currently included in rent)

710 Tax

600 Insurance (seems a little low to me, but that is what the owner is currently paying)

1440 Capital Expenditures  5%

1440 Maintenance 5%

12260 Total Expenses

16540 NOI

7.5 % Cap Rate

25% Down $55000 

30 Year loan @ 4.5% $836/month $10032 Debt Service

6508 Income per year 542/month 

11.8% return on my investment of $55000

Does anyone think this building is worth buying?  Would it be worth buying at 200K or 180K?  

Thanks in advance for your comments.