I would recommend considering conventional financing until you reach Fannie Mae's limit of 10 properties, then consider either a portfolio loan, and start your race to 10 again, or look at DSCR at that time. 

What are the limitations and benefits?

You have a limit if it is an ADU.

In our still relatively limited experience, seller financiers are usually looking to get a higher asking price in exchange for the favor of the private loan. 

The fact of the matter is, when you sell or buy a business, you are entering into a business partnership with the person on the other end of the transaction.Yes, the partnership is limited (partial buyouts aside), but what you will be accomplishing during your time together is significant.Due diligence can take months.

Cozy has been acquired by apartments.com, and will not let me sign up for cozy, and the functions seem limited.

Not the entire 700k can be offset because of the 461 limitation.

This allows us to participate in both pushing rents while also limiting vacancy exposure.

These properties appeal to students and low-income renters, especially if traditional housing is limited.

Your income isn't high enough for it to make sense as a rental and the closer you get to your residence limit the greater pressure you will have to sell it before losing your exclusion in whole or part. 500k right now can make $15k per year income with zero maintenance or tenant risks.