heres my input on the skimmer/scrubber debate.
personally if i was to use one or the other, it would be both, however im very fond of the skimmer. i DO NOT have experience using a scrubber but heres my thought. a scrubber grows aglae which feeds off nitrates and phosphates, a skimmer breaks down nasties bonding them to bubbles removing them from the tank. if things are done right and properly (with a skimmer, right depth sand bed, flow,not overfeeding. . .) there should be 0ppm nitrates to begin with causing no need to grow algae. just my take on the subject.
as for the sump i personally like to split the line coming down to have PVC going to either end of the sump. one side the refugium the other the skimmer with the return pump in the middle and bubble traps.
what size sump is this going to be? do you have room? because rubbermaid stock tanks make great sumps and come in large sizes.