There'd be minimal furnishing costs, as I'd leave my current furniture in there (i'd move somewhere else furnished).Given this, what are the cons I'm not thinking about?

You will need to be shuffling furniture around a lot.

I tell her that I am not a full, I understand what the seller is doing - trying to push a holdover tenant (with little children - in MA!

I want my in laws to do the house hack cuz I cannot move from where I live with my spouse and children. 

Essentially the entire housing market will shrink as a whole, along with all of the ancillary businesses that surround RE - lending, moving, furniture sales, auto sales (yes, a lot of auto sales are based around housing changes), realtors, Lowes and Home Depot, etc.

I have 3 children and my oldest son's father was killed when my son was 2 years old.

Or is it sufficiently affluent that many send their children to charter/private schools and the public schools are suffering further decline as a consequence? 

Most banks in Norway that I know of give you better interest rates for mortgages over 2 million kroner, so I would try to place myself in that category if possible.Another thing to concider is that there is a law here that let you take up to 15% of your rental income and make it tax free if you rent out your flat with furniture.

This can be done not only by raising rents, but adding income sources (covered parking, garages, vending machines, storage lockers, furniture rentals, corporate units, student housing, premier amenities) and lowering expenses.

Get a STR policy, will cover guests trashing your place, vacancy if there are any repairs needed, furniture