It looks like the garter stitch buttonbands are "knit it" as you go across the rows (not knit onto the fronts after the fronts are done). Correct? It looks like it.
If the body of this sweater is knit in 3 pieces...that is to say...the Left Front, the Right Front, the Back...I always start with the Left Front even if the pattern says to start with the Right Front. Why? Because the Left Front has no button holes. When the Left Front is done you have a clear picture of the number of ridges in the buttonband. Then I use that as a model to place the 'built in' buttonholes on the Right Front, evenly placed just where I think they should go.