With proper husbandry you should be good for a long time. LR and LS will absorb chemicals and medications so never ever ever medicate your display tank. Also you should have enough critters to stirr up the sand bed to avoid dead spots in the sand. Starfish, Nasarius Snails Gobies, etc will do that.
i was thinking to use a 20 gallon sump. can i put return pump, heater, LR and skimmer without making one portion for each item. did i just make sense? hehe
Are you saying a baffle for each item? You don't need a baffle for each item. You can have a HOB filter/UV/heaters/skimmer all in the same baffle, If you wanted. As long as you have room for everything.
Is that what you were asking?
EDIT: You'll want the return pump in it's own baffle because the water will be the lowest there and you don't wanna have you heater and skimmer out of the water...