I work as a Firefighter full time in Richmond, Va and would love to supplement my income on my days off.

No, if a mortgage was recorded, it would have to be paid off, or the holder of the mortgage would have to agree to an assumption, or to write a new note/mortgage with the new buyer.

Cash flow is better here, but appreciation is less (CA is off the charts for this metric compared to most of the country, so it's not that OK is bad- depends on your goals and expectations). 

Absolutely, what sparked my interest is several homeowners have asked  my GC friends if they could build ADU' and sell them off.

They are the only member of your team on the ground that doesn’t earn their living off of transactions.

It felt very cult like and put me off massively.

You'll have them paid off by the time you retire and will enjoy a significant boost to your retirement income.Generally, you want to grow your portfolio wide (more units), before you go deep (paying off).

I walk into the house with my binder of all my needed contracts and if we come to an agreement I fill out the contract right then and there. your the man  I love it.. when I started I did my deals on the hood of the car and my contracts were on NCR paper so I just ripped them off their copy :)  my contract was also just one page and included escrow instructions..

When it comes to cash flow versus appreciation, there's a bit of a trade-off.

And it’s all tax free income on the side due to all the real estate write offs.