Turing a duplex to a triplex

[Jordan Craig]

Hi! For a bit of context, my wife and I recently moved to Tennessee and after renting for a bit we are just about to close on our first property. It's a duplex in Chattanooga (technically Red Bank) and we will be house hacking for the next couple of years to build some momentum and experience. The property is a duplex on a street entirely full of duplexes and even a triplex or two. 

The basement is empty and we are looking to finish the space and turn it into another unit. Since I'm a contractor and we will be living in the property it will be easier to pull permits for the work. What steps do I need to take to make sure I can get this going as smoothly as possible especially when it comes to resale in the future? Should zoning be the first issue and what steps are needed for that? Should it be utilities? (Both of the current units are separately metered) Would it be something else I've missed?
Thanks in advance!