Owner financing with bridge loan as down payment

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Exit strategy for 2-3 year bridge loan as down payment?  The numbers below reflect my best estimate WITHOUT bridge loan paydown.  Has anyone used a similar method, or can advise if this deal might be worth the risk?

I'm close to making an offer on a 20 unit MF in a Houston suburb.  It's owned free and clear, and the details of the situation lead me to believe the owner would be interested in owner finance.  

I have excellent credit, a 126k salary, plus about $30k of my own savings.  I'm interested in pursuing a bridge loan as a down payment for the property, then using my own savings as operating costs (emergency fund).  The property is 100% occupied, but I still factor 15% vacancy rate as the Texas standard.  Built in 1980's, some deferred maintenance, have not done inspection, I expect surprises--but since it is inhabitable I do not plan to make any value add changes until the bridge loan has been paid off.  My wife wants to manage the property, but I've factored in 8% as a contingency.    

Offer: 550k w/ 55k down

Closing cost estimate: 15k

Financing: 4.5%, 20 yr amortization  

Gross Monthly Rent: $9975

Yearly Vacancy at 15%: $17955

Mortgage paydown: $3131

2017 Property Tax: $9000

Yearly Management: $9576

Insurance: $3000 (really unsure of this number)

Utilities: $12000 per year (also very unsure of this number, I estimated high)

NOI: $5,342 per month

Cashflow: $2,100 per month