Not to nitpick (and I applaud you for taking the initiative to actually make your own parts) but the seam will look much more professional if you make it a double French seam. I used to live with a woman that sewed, if you're wondering how I know.
Google is your friend, but basically at each seam, you put the fabric right sides together, leave 3/16" or so at the edge and sew together. Then, fold back the two 3/16" edges, flatten them against the piece they are part of, and sew them down flat. What you see when you turn the piece right side out is the leather butted together at the seam and a row of stitching on either side of the seam. Look at pretty much any leather car interior. A Mazdaspeed Miata, for instance, has this stitching on its seats.