He must’ve called me three times a day for a week straight, worried he’d mess up some timeline or trip over the identification rules.

We're planning a trip this spring.

I have read the city’s guide https://www.slcdocs.com/Planning/Guides/ADU_handbook.pdf but I still have questions.1. can tell that till require the owner to live there for the ADU. 1a is it for permanent residency or is it justified if it is a second home that I would use occasionally?

BiggerPockets is a great place to find featured agents experienced with long-term rental investments—they can guide you to cash-flowing properties and connect you with resources like contractors and property managers.

We arranged closing during a slower period of time & had him leave everything (furniture, inventory, guides, etc.) literally bought it & could start taking booking the same day.

It could be worth reaching out to some local brokers to ask them, as they may be able to better guide you. 

From screening to security deposits to eviction, recent laws create many ways for owners to trip and fall.And now Multnomah County has prevented landlords from evicting delinquent tenants.

Pretty much the core of the STR business.Higher your rank gets, you can increase your price and be more picky in selecting customers which usually lead to a better review / less party or complaints / less expense and higher profit with a happy life.I know some people will argue, but the ranking system is the truth and should be the only guide to your STR journey. 

Next, I'd start looking for a market that will fit your needs & do some research on the market's economic divers / population rates & other things pushing the market to grow & take a trip out there to get a lay of the land. 

No, banks do not allow a seller held second now a days due to risk and new guide line changes.