Without a third management entity, I would conceptually have to duplicate everything... for instance, two accounts with my tenant screening service, two Home Depot credit cards, which entity pays for a major tool purchase that will be used on both companies?

No matter how carefully you screen tenants, they might still wreck your place or cause you a lengthy or expensive eviction.

Our theory is, if we continue to buy in beautiful association communities, and continue to screen our tenants and get strong deposits, we should continue to have the tenant history that we have had, which is phenominal.

By definition the records are not in one database as the courts are generally organized along county or state lines.Have you googled for tenant screening services?

Yes, NNN is somewhat passive, however the lease renewals typically make landlords blood pressure go up.

4) How do I screen DST's?

I found the underwriting to be sound, and the sponsors professional -- but I used a broker who did thorough screening of sponsors on my behalf.  

---So, learn the neighborhoods where you plan to invest and use Google Streetview to virtually explore them.3) Poor Tenant Screening - they typically can't sell a property until they place a tenant.

I would screen as many properties as possible via online and through phone calls, and lastly I would fly out to the property for a physical inspection before I ever put anything in writing. 

They will be there to give you advice on properties and neighbourhoods, to oversee renovations and repairs (making sure they're done promptly and properly), doing inspections, screening tenants, collecting checks and evicting if necessary.