Am I nuts or there's real potential in these 14 duplexes

[Abad Marroquin]

First, I had these 14 duplexes under contract for $450K. After I walked the property, found a lot of deferred maintenance, learned that half of the units are in the least desirable part of town and around $100k in repairs and updates. They were collecting about $6,500 in monthly rent, way below market rate.  The insurance estimates I got was $900 annual premium for each duplex (at $140K replaceing cost). At this point the deal did not seem promising at all.
 

 Then I was able to convinced the seller to reduce the purchase price to $300K (33% less). 

Also, I learned that the county has appraised it at $570K for tax purposes. At the same time, I was able to find an insurance company that quoted each duplex at $457 annual premium (insuring each duplex for $60k with $1000 deductible and $500k for liabilities). This is half of what the other insurance companies had quoted me. The reason I am planing to insure this duplexes at $60K each is because I am purchasing them at $21.4k each. I plan to invest  around $10 in each, so basically I will be spending less than $35k for each duplex. I plan to rehab them with an employee.  I think insuring it for $60k should be ok for now (let me know if I am wrong on this). 

At this point I plan to buy these 28 units with a loan of $400k. Purchase price is 300K and $100k for updates and repair. I plan to gradually fix up the units and then raise the rent progressively until we reach market level which is around $425 for 2bd/1bth a month and $500 for 3bd/1bth. I expect to accomplish this in about 2 years.  

When I run the numbers using 10% for vacancy, 10% for capex, 10% for management, 10% for maintenance and repairs, $550 for landscaping, propetry taxes and insurance I expect to get at least $$2,500 in monthly cash flow. 

Since the county has appraised these 14 duplexes at $570K with all the repairs they need, I would expect them to appraise between $700K and $800K after rehabbing them. My plan is to refinance in 2-3 years and get at least $200K to continue investing. I know I will have a negative cash flow the first months but I expect to break even within 5 months. I plan to invest most of the cash flow from then until I fix them all up. 

Am I missing something here? My banker thinks it's a great deal. They have approved the $300k loan and $100k for rehab.