Are they paying below market rent because the landlord hasn't increased rent over the years (eg long term tenants with no increase) or were they rented that way (ie low rent either to fill or because landlord didn't know what market rent was)?

Now is the time as my wife and I have further discussed short term rentals and such recently.

It can be done with FHA loans, short-term rentals (Airbnb), long-distance landlording, live-in flips, or partnering with family.

This 1br1ba basement unit generates $1,800/month so I'm trying to keep it under the radar for as long as possible, especially since I have such a great tenant in there.I recently had vacancy in 1 of the units in my house which is a 3br1ba.

Question: If we have a tub in the master bathroom, but not in the hall bathroom, is that a deal breaker for turning the home into a mid term rental?

Yes absolute is a term in the industry. 

Maybe long term it will incentivize more building, but we're already building at a very fast clip. 

The long term trends with jobs and population growth are still very strong.

I would wager that if you haven't sat down and done a tax plan before, spending a few hundred dollars with a tax pro could save you tens of thousands in the long run. 

Ours dried up in June 2023, and even that was ridiculously long.