Duplex Conversion thoughts

[Edwin Rodriguez]

Hi I have a single family home that I would like to turn into a duplex.  the home  has 3 bedrooms and two full baths.  the owner added on a master bedroom, full bath, and huge walkin closet.  The addition runs down the entire side of the house.  It has its own exterior door and another entrance into the master through one of the other Bedrooms.  I would seal that door way off to make it a studio apt.  The addition was done in the last 8 years.  

Like to get some thoughts on cost of splitting utilities vs including it in rent, experience with adding on the additional mailing address and anything else anyone can think of that I should be aware of when taking on this project.  

Thank you!

Edwin