Quote from @Marlena Hawkins: Does anyone know what insurance (liability, E&O etc.) is required for Property Management companies in DC and Maryland? 

You can always hire a different PM company.

Keep in mind if you are renting a house to a company you can write whatever you want into the lease. 

As far as a flat rate, I would talk to companies offering services as mine and ask. 

For active investments I advocate considering how you can diversify WITHOUT ceding your competitive advantage nor the superior profitability of the niche your in.As an example my business is running an investment fund and syndication high interest commercial mortgage loans secured by income producing real estate. 

The SMARTEST thing I did...was follow a "who" not a brand or company or model or some "thing". 

I personally believe single family produces the best rents and appreciation.

There are companies also that just tunnel. 

Built a 20 person company around our own portfolio.

I work for a wholesale company that does 10-15 deals/mo in Alabama.