I understand the debt to income ratio concerns, I was thinking maybe I could place them under a LLC or INC and or not be too worried about that if I am in the six figure bracket.

I also make sure the have legal documents to protect their investments, such the real estate itself.

Even then you run the risk of the appearance of a conflict, and the resulting potential lawsuit.The conflict arises because of the different legal roles of an agent and a principal.  

Big drivers are the hospital/healthcare presence between Sentara, Eastern Va Medical School, and the children's hospital, also easy commuting to downtown Norfolk for banking and legal, AND you're a stones throw away from the largest college in the area, Old Dominion University.

I want to purchase in America, I read that it's legal for Non-US residents to do it.

Not a legal advice, but AFAIK you cannot mix IRA funds and loans unless your IRA invests in a security and not in a property directly.

I mean, hypothetically under what conditions/criteria would YOU finance someone's down payment as a debt partner?

It is in my opinion a necessity or you become a legal target.

I have thought about vacancies, updating costs, and maintenance costs along with legal and leasing costs.

Any cost effective solutions out there for how I can fairly and legally get the tenants to pay for their own heat?