I am in a unique situation in which I’ll be moving from Hawaii back to the mainland within a year after selling my business, and I’m trying to figure out where to move to.

This will vary greatly from person to person, their unique situation, comfort level with debt, etc. 

While the Solo 401k has eligibility requirements, it also has some unique benefits compared to the IRA.

Be careful to establish a price per sq ft that was derived from similar properties, definitely not the price per sq ft from the regional data, and even then it's still just a ballpark indicator, as all property is unique in its own way, and will have elements of value that are not related to the size of the home.

seeing ~$600+ / mo for some of these complexesin terms of short term rentals ... do you know of any unique restrictions, laws, battles over short term rentals in any specific areas?

It's a unique space, and not my strategy it's the way the property came.

Here is the unique situation.I live in my parents house by myself as my parents live in Europe.I take care of the property and two other rental properties.

If you're looking to invest in Baltimore then consider both the City AND the County (which are separate jurisdictions, a fairly unique situation that not all are aware of).  

I’m looking for new or unique ideas of what could be done with the land outside of the typical mobile home park, RV/ boat and storage units.

So, in that specific sense, Austin's housing supply problem is not unique.