With your comment "Assuming they are not lying about past projects" is accurate and kept in mind:I would have my CPA go over the numbers, I'd have my attorney tell me about the liabilities of the structure they are proposing and I'd ask the partners what happens if the market changes and everything goes wrong.If all of that checks out to your satisfaction, and you want to be a passive investor then sure, people invest across the country all of the time.Ask your CPA about the tax liability in your particular circumstance.

I am guessing that the way they are calculating is lawful, provided the disclosed APR is accurate and  based on a normal year.

If you can make that MH livable or stayable that would be the best place to start to test out your market before investing any more money. 

Look for sold comps on redfin as you can filter by how long ago they sold, try to stay within six months, pick similar properties and average, if you want to be more accurate make adjustments for different features and finish levels.

I'm assuming my numbers are ballpark accurate. 

@Jay Mat the most accurate way is to calculate each house.

Recommend tested.

If a Joint Venture fails the Howey test, you will have committed a felony. 

Finding and using accurate numbers really helps.

In chatting and building the relationship (I’ve been helping repair some things around the duplex), he’s the one that has been discussing moving on with the property and the thought of owner financing, he mentioned the tax benefits of it all.Now he could just be testing the waters to see how much I know and what I would be willing to expose, but he’s definitely keen to the idea of it all...I guess overall I’m eager because I know the power of this property, and the willingness of information he’s been sharing with me.