The only adjustments I made were adding a couple additional rows of data at the very bottom of each page to track what I paid in principal each month, and what my net cash flow after that was.

If you're looking for STRs on the beach, you'll have difficulty finding something that cash flows unless you can get optimal occupancy. 

HOWEVER, I do personally make over $100k/yr cash flow from 16 properties here.

The land is twenty acre parcel, which if we buy it, plan to hold it long term to develop either residential or commercial with partnership or cash out for retirement.

Are you cash flow positive on the rental at the moment with that rate? 

My main concern is the limited cash I have available for the down payment and renovation costs.

Better yet cash out refi? 

My strategy would also be going for more price appreciation than cash flow. 

Always have a cash reserve on hand, maybe twice what you think you'll need.  

Finally, other tax deferral strategies prevent you from getting immediate cash, and your stated goal was to get cash for a down payment.Either this firm does not understand what you're hoping to accomplish or they are not being straightforward with their promises to you.