If you're looking to retire in a few years and you want a simple zero hassle lifestyle perhaps a REIT or a solid stock/bond portfolio would be great.  

If we can mitigate that so that we make sure that we earn our 9%, then we would be willing to take a look at that deal knowing that our upside is worth the risk.With respect to SFR, you need to factor your time as an add on to the return.

Wow factor or a white elephant?

Unless they made lifestyle changes and cut other monthly expenses, assistance in making their mortgage payments is not going to solve their problem.

The other thing to factor in is job stability.

I'd factor in a slightly higher vacancy for that type of property. 

What other numbers/factors do you recommend I look into?

Below I've copied text from Pub 523 - Selling Your Home-------------------------------------------------------------------------------------If you own or live in more than one home, the test for determining which one is your main home is a “facts and circumstances” test.The most important factor is where you spend the most time.

I would like to buy another house before the 2 years of rental income is factored in...what are some of my options considering we do not have enough to buy a house cash? 

(And I would factor in some expenses in your calculation like maintenance, etc).