I'd talk to some investors experienced in sub-to, and possibly an attorney. 

In my experience, 80-90 percent know nothing and have nothing to say.

You need to be careful with prequalifying people these days as various cities and states have laws that can restrict that. 

But well done getting your foot in the door.

But IF the property in question is in compliance with all code, and provides a safe and secure environment, all problems are timely addressed and corrected, and the property is maintained on a professional level, then the investor who has a large capital investment in the property should be entitled to enforce any contracts providing him with the agreed to cash flow. 

I noticed you are in Austin Tx (I'm in the Ft Worth market as a Landlord, rehabber primarily). 

What is the best way to use this money from 403b accounts from previous employer for real estate?

20 to 25 year amortization is pretty standard for commercial loans, in my area at least.

However, lenders want to see the additional guarantor receive consideration in return for their guarantee.

@Andrew LaxWishing you the best on the sale of your portfolio!