I run my 90 gal
reef just as you have described. LR
, skimmer and ample powerheads for water flow. Other than the carbon in the skimmer housing, I run no additional filtration. Sand bed is no more than 1¬Ĺ".
If you have the ability for plumbing a sump it is definately a plus for added water volume and for housing unsightly equipment (heater, skimmer etc...) but it's not going to increase filtration capacity.