Tax and legal implications of 5+ units

[Stephanie W.]

I have a six unit under contract. It is my first 5+ property. I have two duplexes and four single families and manage them all myself.

Are there different landlord/tenant laws that only kick in once 'commercial property' status kicks in? 

Are there any differences in the tax code for a 6 unit as opposed to a duplex?

Lastly, do any special legal issues arise once this threshold of units is reached?

Thanks in advance for the input.