1,2,3 good. Don't do 4... you'll look like a jackass. Not that it matters, because so little emphasis is places on the
SOP. Just explain your interest in economics, and maybe quote some papers... explain a bit about an area you're interested in (like 2 and 3). However, 4 will make you look naive, and (if they read it) the ad coms will be slightly condescending and dismissive of the notion that you *really* know what econ research is about.