Analyzing my first deal (help!)

[Swetha Mandava]

I'm investing in a duplex in Squirrel hill, Pittsburgh, PA

Offer price 253k
downpayment 25% = 63.25k
Mortgage Rate 5% ARM loan with 7/1
Current Rent, fully occupied 2125 / month
Vacancy Rate 6%
Operating Costs 10%
Property Management 7%
Insurance 1500 / year
Taxes 5800/year once tax assessed value increases to sale price. Currently 2.5k/year.

My vacancy rate + operating costs are general estimates i found on blogs. It seems to be a great location, very close to CMU so i estimate vacancy rate should be much lower in reality. Although, the house is somewhat old with a 10 year old roof.

With the above estimates, I'm bleeding -142/month. That seems worrisome with popular advise but unsure if i could increase rents in a year?
The inspection report just came back with 2 things i'm worried about - the house has a fuse box and might need replacement and the foundation wall that has been repaired about 17 years ago has a crack in it. The seller insists both are nothing to worry about, getting an electrician+structural engineer to take a look. 

Any advise on negotiating price if repairs are needed? 
Thanks in advance.