What to look for in duplex investing?

[Nicholas Lehman]

Hello

I am fairly new to the investing world having just bought my first fourplex last year.  Recently the duplex across the street went up for sale and i am thinking how nice it might be if i could get it for the right price.  They are asking 365k and the one side that is rented goes for 1400 which includes all utilites for the tenant.  A potential lender told me if i put 10 percent down my mortgage payment would be about 2300 with todays rate and counting for pmi.  Just curious how good/ bad this deal is given there is still vacany rates, maintenance, cap ex, and other monthly costs to factor in.  How should the numbers play out in a duplex and what would be a good offer price to make deal worth while?