Is my math on this okay?

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Hey, I’m new here. I’m 38 and live in North NJ and currently own a 2fam in which I live in one unit. I bought it on a whim 10 years ago and have been relentlessly paying down my mortgage... 6 years left. I work as an ironworker in NYC by day. In the past 20 years I’ve never missed more than 1 week of work in any given year and have made no less than 40 hours a week every week. I’ve got a decent savings now of about 200K. 

About a month ago I busted my ankle, four fractures and ligament damage. Sitting home this past month, which I’m not used to, I’ve been searching investment houses near by. I’ve decided to find multi family homes and come up with an offer based on 8%> of my total out of pocket. I’m trying to use what I believe to be a cash on cash formula. I’m just taking every expense minus the income (annually) and dividing it by the total out of pocket money I have to come up with. 

I found a 2 family house in town that just came on to the market. It’s kinda beat up and needs some work. I’m pretty handy, I’ve done most of the plumbing, electrical, carpentry in my own house among others but I still plan on outsourcing most of this work and I’ve placed a number on everything that needs to be done. Here are my numbers: 

325K asking

2 fam 3br 2ba

40K renovation costs

15K closing

PITI:

275K offer (I want to buy it for this or less)

55K down / 20%

4% interest

10,500 tax 

1500 insurance

Payment: 2100 / month

Rent: 3000 / month

NOI: 900 X 11 = 9900 (1 month vacancy)

TOP: 110K

COC: 9% (9,900 / 110,000)

I’ve over estimated the tax, insurance, closing and repairs. I’ve underestimated what I should get in rent. I feel like 275K is my max offer based on what I’d like to make. I’m not much of a haggler so not sure if I should come in for less first. 

Do you guys think I’ve analyzed this properly? Thanks a lot! -Ray