What you are talking about is a tiny home which addes even more levels of difficulty in getting approved.

When it comes to individual properties, maybe—especially if you don't have an experienced and trusted investment team in place.Before I continue, what is the goal of goal of real estate investing?

My property manager uses AppFolio, which is fine for transaction level detail and a few dashboards.

My debt-to-income levels, by conventional banking standards, are good but not great.

I haven’t heard the story of  the investor who rode the coat tails of a wholesaler to the same level of success but networking and building relationships with wholesalers seems to be prioritized over all others industry participants. 

I don't know your experience level but if you don't have time you could play the numbers game and carpet bomb the whole neighborhood.

Trust me no one is going to get into seller financing for a rate cheaper than market rate.

This means the crime level shouldn't be high, the median income > $40K - $45K, and there should be enough homeowners in the neighborhood.What else I should care about?

That's next-level.

As an extra level of protection You could try and save up a few months of what the potential mortgage will be to give you peace of mind.