Snowball Payoff 10 SFRs in 7.5 years for $110k cash flow - advice

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I'm considering a purchase of 10 SFRs in Wichita. I have a few homes there already, and a fantastic property manager that I respect and trust.

I've run some preliminary numbers, and it looks like I might be able to cash out refinance my home at 3.75% which raises my mortgage payments by $350/mo. I can then finance 4 houses on 30 year fixed FNMA loans. The remaining 6 houses will be on a 20 year amortized commercial loan. 

The plan is to take the net cash flow from all 16 props I would own and apply about $4000/mo against the commercial loan, with estimated payoff in about 4 yrs. Then I apply the $4000/mo plus what I had been paying on the comm loan against the four FNMA loans and they should be paid off in about 3.5 years. 

Net cash flow from all 16 properties should yield about $110,000 / year, and it will take 7.5 years to get there. I'm relatively comfortable with the Wichita market, although it is not my own market so I dont know it very well. I've spoken with my bank there, my property manager who owns 100+ homes of his own in this market, and a couple of realtors and they all feel comfortable about this move.

My question is this: without getting more specific about the actual numbers on each property, what are some risks I may not have considered with this approach? If my income were to drop by 25% and 6 houses went vacant at one time I have reserves to carry me for about a year. I see this approach as less risky because I am paying off a property every 12 months or so. 

Who else has used the snowball method of paying off rental properties? What can I learn from you?