It all depends on how you'd like to plumb it. It's personal preference. In my setup I did not put bulkheads on the sump, why the added expense? Yes it looks nicer, but it isn't needed. My flex PVC lines just run into the top of the sump and go to the bottom. I use a cable tie to keep them from going anywhere.
You may want to divide up your sump into compartments, again, personal choice. I like having the refugium somewhat seperated with a partition so the caulerpa doesn't end up growing on the return pumps, etc, it helps keep things tidy and limits the amount of microbubbles. I have my overflow split, half goes into the refugium and half goes into the chamber with the skimmer.
My 20G sump has 3 compartments, one for the fuge, one for the skimmer, and one for the return pump. I keep the heater with the return pump as thats where the most of the flow is.