It is also stated that commercial and residential real estate are not supposed to be part of the same enterprise. 

The following requirements must be met by taxpayers or RPEs to qualify for this safe harbor:Separate books and records are maintained to reflect income and expenses for each rental real estate enterprise.For rental real estate enterprises that have been in existence less than four years, 250 or more hours of rental services are performed per year.

The last time I rented a car from Enterprise Rental, I signed their agreement and would never thought about asking them to change it.  

When I first read The Intelligent Investor by Benjamin Graham, for example, I just had to be the Enterprising Investor and not the Defensive Investor.Now I look for good investments that generate a sustainable positive net cash flow.

Any direct or indirect transactions between a plan and a disqualified person create severe tax consequences.Your Solo 401(k) can invest in rental property, but must do so in a way that has zero intersection with you or your personal enterprises.  

A lot is going to be on the horizon for me (Swan Enterprises) for sure :) 

Unless you're making a living off of real estate only, many people use real estate as a way to leverage themselves toward retirement and it's a get rich slowly but surely enterprise.1) Larger down payments2) Uglier properties where more sweat equity is possible3) Do as much of the rehab work as possible yourself4) Manage units themselves instead of a property manager5) Rents increase over time, mortgage payments stay the same, cash flow increases over time.6) Appreciation is more important than cash flow

I am currently set up as an LLC (Ezer Enterprises, LLC) specifically for many of the reasons you mentioned, but you definitely caught a few that I had yet to really think of!

For the smaller owner (less than a few hundred units) there is the SmartMove solution and for larger owners the enterprise Rental Screening Solution. 

private enterprise is trying to help.https://www.msn.com/en-us/money/realestate/stanfor... when you have median home price at 1.2 million for a house U could buy in Cleveland for 100k.. you can see the issues.