Some boot makers start with the outermost row, but I was trained to begin with the innermost row. It really depends on what style of design you’re doing — with this one, accurately defining the unstitched space in the middle is crucial, so it makes sense to begin on the inside.
This work is done one row at a time on my vintage Singer 110W that still has the old clutch motor. I learned to sew leather on the exact same style of machine and motor, and it’s like learning to drive on a stick shift. It makes learning harder but once you master it, you can drive pretty much anything.