Do the aquascape then add the fish. Fish will be stressed already and you moving around the home they are trying to claim is going to be even more stressful. At my LFS
they run all their coral frag tanks and one large 200+ gallon mixed reef with just overrated skimmers and biopellets. Nothing else. They do periodic water changes of course which contributes to their great success. I say they chaeto isn't necessary unless you want to grow pods
(but even then they can populate in the DT).