Everything I have read has warned about licensing/regulatory issues only if I am lending to owner-occupied.  

Typically families occupied main house and younger renters often in the casita. 

My wife and I are still in the 'learning phase' as real estate investors, but we know for sure that in the next year (a) we will be converting our primary residence in to a rental, and (b) buying another house that will be our primary residence for 1-2 years so that we can qualify for an owner occupied mortgage.

I am ready to retire and looking to invest again to occupy my time when I retire.

Did I properly estimate the cash not only to buy the property but also the six month reserve funds that some lenders are requiring for non owner occupied units?

This is an essential tool for anyone buying a tenant-occupied property.

How long do rental properties typically stay on market before they are occupied with a tenant?

We bought a 2nd home 0 money down that we are occupying and about to have it up on the rental market in the next few months to make our second property, then back into our RV we are going.

For example in many jurisdictions I can STR units in a duplex but cannot STR an ADU (some jurisdictions will let you STR if you owner occupy).

And in fact they may not cover homes not occupied by the homeowner.