As I expected, last month, they suddenly needed to vacate after 9 months due to a few sob stories (in reality, they were students and school has just ended). 

If you want to look at 600 a month rentals then I have seen student housing and also multifamily that is retirement type communites for lower income seniors work well.Students the parents are often on the hook for the lease guarantee and with seniors most stay a really long time as the small space is something easy to manage and they do not like moving at their ages.

I am evaluating a SFH that is zoned for a duplex, and already has separate entrance, 2 kitchens, and 2 bathrooms because it is currently used as a student rental.

I'm seeing a Schedule C sole prop business in your future tax returns, called something like "Erick Vallejo College Student Hosting & Support." 

Currently remarried to the love of my life who brought with her around $45k in debt of student loans.

I rented out a room and even Airbnb'd my room in order to pay off student loans and save money for another property.

You can approach it a couple of different ways:  if you are renting to college students, you can choose to rent either the entire house or rent by the room/student. 

However, I am conflicted on whether to invest in a college town where properties are a bit more expensive but will for sure be rented out by students with parents on the line as co lease, or in Toledo where property prices are a bit cheaper but finding tennants may be a bit tougher with more expenses.

My wife is also a student graduating in August.

Keep in mind these are college students and I don’t see them renewing as it’s their final year.