Takes up too much space to write it twice with minor adjustments... Once you've done a cardigan you'll understand how they're put together and where shaping should go.
Anyway, yes, the side seam edge is where you do the decs, same as you did the decs on the back. That will also be the same side for the armhole shaping shaping. There's at least a drawing/schematic of it so that helps; not all patterns provide one.
sue- knitting heretic