Hidden Costs To My First Duplex?

[Dan W.]

I am looking at pulling the trigger on buying a small duplex in Baltimore Maryland. Rough numbers are $95k sale price, and rent looks like about $1000 for one unit and $800 for the other unit as is with no up front costs. 

The 25% down payment is no problem for a conventional loan, but until it is occupied and operating well, I wanted to reach out to the BP Community to see what other expenses I need to account for right from the start until it's occupied. If I need a buffer, how much is suggested?