I searched for properties that stay on the market for a long time.

Would you think changing my minimum stay on Airbnb would be worth it?

You might get the dregs staying at your place and you don't want it trashed.Make sure you list it on VRBO and AirBNB for maximum exposure.

Despite the equity We also want to take advantage of tax advantages we did stay in the property for 2 years !  

Sure it does. but depending on who the celebrity is/was.....That's why so many little hotels, boarding houses, vacation rentals, etc..... feature this in their advertising.And in some cases, you will not get more money, but you will get more guests.A little while ago, I went to Tombstone AZ and stayed in 'The first boarding house in Tombstone'....really cool place but kinda small and, well....old feeling.

We primarily focus on residential multi-family and so far we have stayed in the Western Mass area.

So, even when the market is challenging, you can still see properties and stay current.Don't take a break when the rates are high.

I can't see what you would need a course to teach you that you can't learn by reading 30 Day Stay; listening to the BP podcast episodes with Sarah Weaver, Zeona McIntyre, and Jesse Vasquez; and hanging out in MTR forums/Facebook groups.

If the tenant stays, they will be on a month-to-month lease, which requires a 30-day notice.

Those failures are  more negligent than a PM allowing a guest who paid with expectation to stay at the house to remain there in the middle of winter when they arrived on a Friday evening as you described.For now you will have to rely upon insurance, I don't believe the PM acted unreasonably given the circumstances.