I'm wondering if there are companies similar to Memphis Invest that have turnkey investment services for 2-4 units (ideally 4plex) in US real estate markets with solid underlying economic fundamentals.

Austin appreciation is based on solid market fundamentals, as @Jake Panko has pointed out.

Real Estate investing is a business that can be tough, but very rewarding if you have a great understanding of the fundamentals of Real Estate Investing paired with good sales & negotiation skills. 

I haven't done these in your area but the fundamentals are the same. heck with city zoning to be sure you can do the project.

The reason being is that I think those two markets offer the best combination of affordable prices and strong rent ratios with good economic and demographics fundamentals.

Every property has a valuation, trust me if you reduce the price low enough someone will buy it unless there is something fundamentally wrong with it in which case you donate itYou mentioned that it doesn't cash flow even though it's paid off???

The "Duplexes of Texas" builder has been the only fundamental driver in Buda. 

It isn't market cycles that tend to get investors in trouble, it's ignoring the fundamentals and using ridiculous financing options that can't handle market stressors. 

3) That depends on your NOI minus debt service which depends on a variety of factors such as market fundamentals, job growth, demographics, what can they pay for rent based on their income and much more.I, for one, don't invest in areas with a population less than 250K and we're about to raise that number soon.

Obscure markets don't usually have enough of an economic engine to bring you rents you're looking for anyways.Make sure a market fundamentally meets your investment criteria first.