Why is it that most “authorities” that ban STR (or heavily regulate) decide to ban or regulate rental “30 days or less”?  

As Jonathan mentioned, this is a technique for experienced investors, not something a beginner should play around with.

Just your basic 20% down get a loan, etc.I know there are 84 other variables that come into play in making the decision.Does the think tank here have any general pieces of advice?

Having said that, they know how the game is played and that they are messengers for their clients whether that is the buyer or seller.

The safer play is to use financing with healthy contingent reserves built into the loan.The other reason why I recommend using financing (and believe this is more important) is the banking relationships you will build through the process.

You can use a BP calculator to play around with scenarios. 

I just don’t want kids to play with it or someone to set it at 60 trying to cool it down fast, and then forget about the setting.

Now is the time to be investing in Wenatchee, Washington.This year the area's first Hydrogen plant is scheduled to start operating a $25,000,000 project.Northwest Natural Gas is putting in a $43,000,000 natural gas plant.In May of this year, the Washington State Port Association awarded The Chelan Douglas Regional Port Authority The 2024 Job Creator Award for creating jobs in the area.Earlier this year at a state of the economics luncheon it was rumored that the area will have over 25 data centers in the future.I was recently at a community meeting where Helion Spoke about putting in the world's first Fusion plant.

The new government is revoking these rules but only to transfer the decision to the local authorities.

It's very hard to play the game of real estate without it, and I'd encourage all new investors to work hard to maximize their income upside, and work hard to get into a stable position before obliterating your DTI on a capex nightmare.