I could just invest in an established REIT, but where is the fun in that?

It is correct to say you cannot contract prior to 18, HOWEVER, nothing says you can't establish an LLC and contract on behalf of the LLC.  

We recently started a private equity fund to raise/pool capital to buy larger pools of notes and scale up the business now that we have our basic operations established.

Establishing any funding entity is not a license to originate mortgages.

Talk to them, explain what you want to do, and find one or two with which you can establish a long-term relationship.  

Once I established a lending relationship with a 3-location local bank, I've been able to do cash-out refinances numerous times.

My husband and I are in escrow on a new primary residence that cuts both our commutes in half, is in a more established community, etc.

@Juan Diaz modular home industry is very well established on the mid atlanatic markets.it has never been that well received in CA..

Anything you can do to establish your business credit profile and improve your personal FICO will also give you more options. 

You will be better served to re establish your personal credit.In order to start rebuilding credit, the most pressing time-sensitive matter is to establish long-term open lines with good payment history as soon as possible.Open a secured credit card with a limit of 4x of a regularly recurring bill - cell phone, water bill, etc.