Adding a Duplex to a current lot

[Tyler Ebnet]

Last summer we bought a duplex in Marion Iowa and it has been a great investment so far, but we have been toying with the idea of adding another duplex on the same lot.   The lot has plenty of space in concept to put a side by side duplex on similar to the one that is already there, but this is a new undertaking for us.   Looking for some advice that we should be looking out for when planning to do this project.   Where should we even start with at the city?   And drawbacks that we should be looking out for?   

Thanks for the advice

Tyler Ebnet