I own a roofing company in Denver and a separate gutter company there too. 

I have one rental in RB and a few in Memphis which i will probably be selling soon since I can't seem to find a property management company that I wouldn't mind working with.

There aren’t many residential development companies operating at this level, which reduces competition and risk.

After reading Brandon and Brian's book, The Multifamily Millionaire, Volume II: Create Generational Wealth by Investing in Large Multifamily Real Estate, I'm a bit puzzled as to if the GP's must have real estate experience, or if someone can connect enough professionals/companies on their team to execute successful investments.

Waivo is an example of such company.

This is what my company does for our clients..

That is for larger companies or for disgruntled clients or relatives looking to help.Per diems only work in theory.

Timber companies and the feds swap these lands all the time in an effort to create large blocks of either gov land or private timber lands.

Did you self manage or use a Property Management Company? 

My company provides an all-in-one solution for clients.