I have a 60g cube reef tank i want to convert to an octo tank. there are a few things I'm looking for that will determine what species I should get, however - readily available (i'm in az), diurnal and of course longevity. any recommendations? thanks.
There is a collection of links in the Posts with Info for New Octo Keepers thread (sticky in the Octopus Care forum) that should help address a lot of your initial questions (one of the topics is species considerations and availability). In general, trying to find a specific species is often a first keeper's frustration and disappointment. Octopuses have very short life spans and you will not be starting with a hatchling (this is not necessarily a bad thing as they are typically not seen during their first 4-5 months). Most of the animals we keep have lifespans of 12-18 months and you will likely (depending on where you are starting in the cycle) take more time planning for your first octopus than you will have time to enjoy it. I try to stress that you are creating an environment for an octopus and stress enjoying each of the species that you will keep.
On the bright side, it appears we have two recent (in the last week) acquisitions of O. hummelincki and I am hoping this is going to be a trend. Of the warm water species, hummelincki is the only true diurnal local animal we commonly see available but they have been absent from the market for several years. Second on the diurnal list is the imported Abdopus complex group (generally lumped into the aculeatus species but often is not the correct id). Last on the common choices for diurnal will the be cold water, Pacific bimaculoides. Bimacs are typically longer lived but very difficult to obtain and require a chiller. They are not in short supply but are illegal to capture and sell live in the state of California (they only require a fishing license to capture and are used for both food and bait, it is the selling from their common location that restricts their availability).
For a feel for what has been available, look at the top of the Cephalopod Journals forum for the Lists of our Octopuses entries. The species are listed, when known, the source is linked and the animal names will link to the individual threads.