Subdividing Land in Norfolk, VA

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Hi all, I recently purchased a duplex in Norfolk. Its a non-conforming duplex in an area zoned SF-6. It's located towards the front of a half-acre lot. Behind my backyard fence is essentially a quarter-acre of empty land and I am working on ideas to develop it. I'm considering subdividing the land to create a flag lot and building another duplex (if possible) or single family on the new lot. Working on educating myself on the process before moving forward. This is completely new for me. I have attached photos for reference. 

Any recommendations on getting started or if this is even possible?