The loan will likely cost around $11,000-$12,000 - assuming 15% for the year in some combination of interest and points.

Do I have to combine these properties as one deal?

She seemed pretty cool to me, pays her rent on time, but her credit is bad.I agree with you, if a combination of factors make you uncomfortable, then go on to the next one, if you have a next one.

I don't really see the purpose of combining them together (even if you could) as you are suggesting, because I believe there would be more downside compared to just going straight into an OZ fund.

You've overlooked 2 excellent cash flow markets that have a combination of strong cash flow and good economic/demographic trends.

This all-in-one washer dryer combo isn't cheap, but it might help to solve the problem: https://www.whirlpool.com/laundry/laundry-sets/washer-dryer-combination/p.2.8-cu.

In the 2-3 unit world it was always the combined finances that fed into a debt to income ratio and that was the hurdle.   

The property could be located in a crap area.  

When you combine vacancy and leasing: 8% accounts for 0 missed days, 10% accounts for 6.5 missed days of rent.Solution:  Keep your vacancy and leasing fees separated. 

Me and my partner put in roughly, a combined 420 hours during a 3-month process.