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You could start by shecking out the checklist by Colin and Nancy which is under ceph care at the top of the page.
It also depends on what species you are planning to get. For a bimac, we would recommend a 50 gallon even though the checklist says 30. Some of our members have found that their bimacs outgrow their normal size. Protein skimmers and activated carbon will help in the event that the octo inks.
Create lots of dens and hiding places with liverock, you can also put in PVC pipes in as octos like to take refuge in these.