Now we are kicking around the idea of adding an ADU at the back of our long narrow lot to make room for a short term rental.

Wow, that's a lot to think about. 

There is a lot to learn, and if you want to be really hands off, you might consider another avenue.

For me, right now, that was a lot to take on once this disc went out.  

There is a lot to a 1031 but the biggest thing is you have limited time to find a property. 

There's a lot to consider here, but a couple things to consider: there are many brick and mortar banks that offer HELOCs on investment properties, just keep asking.

There is a lot to learn about financing and investing in income properties.You must be 100% comfortable with the information before you step up to the overwhelming aspect of placing all your hard earned money at risk.

After a closer examination you can see from the parking lot to the street there are tire marks where cars have gone in/out of the parking lot. 

There's a lot to consider, of course, such as facilities, HOA, management company reputation, marketing, etc.

I am going to assume it is a older duplex so you should be in Judge Cook's precinct which is kind of like winning the JP Judge lotto !