Congratulations its really inspiring for me , keep us posted if any news arises

If they haven't shown the discipline to save money (with stable jobs) to purchase their home in the first place why would they have the savings in case they lose their job or unexpected expenses arise? 

If you have a banker who knows Single Family homes but she writes you a note on a 10 unit apartment, she'll likely be much more nervous at the first issue that arises because.

How do I protect myself from potential tenancy issues that could arise?

I plan on having an attorney should the need arise.  

What problems could arise by only checking at the local land registry office for land record and and property liens, prior to going to a municipal auction?

Going forward if the situation arises again(hope not), I would explicitly state that the window units draw more energy and the tenants are responsible for any increases.I don't know what type of AC unit you have, but when you say it's "running rough"...rough as in mechanically or it's just not cooling after the repair?

Ways to mitigate risk in a down turn -Manage debt..leverageEnsure you have a buffer/equity Sell some properties in a rising market, no one ever goes broke taking a profit.

So the benefits of a partnership could still be felt somewhat but without the inherent pitfalls that could arise in some cases. 

Have $3000-$5000 saved for repairs to just this house and cover any issues that might arise until I can get that amount accumulated in cash from renting of the house.