Obviously one would still need legal and accounting support. 

I envision this portfolio supporting me during my retirement years—though I still plan to work, just in a different capacity than I do today.I recently finished reading "How to Invest in Real Estate: The Ultimate Beginner's Guide" by Josh Dorkin and Brandon Turner, which has been incredibly helpful.

I might also offer them some support such as a dumpster.

This is why so many people earn large sums of money quickly (lottery, sports, entertainment, etc.) and end up broke.Take Dave Ramsey's Financial Peace University.

Fortunately, the investors I partner with have plenty of room in their lines of credit to support multiple deals and still have a sizeable buffer before they max out the credit.

If you’re making a return higher than a bank CD you can support a mortgage.

The ways around that are to build a business around supporting their voucher and inspection program and spending no small amount of effort ensuring they are smoothly servicing your rentals. 

Support staff at RentRedi were there to answer any questions and help me setup, once setup it runs itself.  

You will also need different levels of staffing to support the various strategies as you are already realizing. 

I went to university in the Midwest many years ago.