Strategy 1: buy a duplex, live in one unit (for one year as a "primary residence) and rent out another unit as a short-term / mid-term rental on Airbnb.

These units are perfect for owner occupants, and they are perfect for related living as you have described.

A couple of years ago, I worked with an investor who never updated the contact information for the loan and the Bank call the seller (ex-wife), that day she was mad at her ex-husband and told the bank her ex allowed someone to steal their property from them and they got no money, she was kicked out of her house and there were strange people living there.This could all have been avoided if the investor did this process correct.Get educated, also I do not know your attorney but not many attorneys have the knowledge to do this process correctly. 

We haven't lived in the townhouse in the last 2/5 years so we would get hit with full capital gains.

This requires 10% down and you typically just have to live in the property for 14 days out of the year.

Did you read Lend to Live?

I live in a rural market and this type of issue with technology may not be as big a factor in urban areas.

You can't rent out a PO box and live there.And yea that sounds like a huge red flag to me. 

Selling would likely trigger capital gains taxes (unless you lived in the property for two out of the last five years or use a 1031 exchange).

I live in California but am looking to invest in Texas, Alabama.