Good Choice
Hey,
I think O. rubescens is a great choice if you have the capacity for chilling, which is sounds like you do. I have had a descent number, and have kept several individuals for up to 8 months before release while doing my masters on their metabolism and its influence on foraging behavior. I have kept mine at 11C, and at that temp they seem to live for a bit over two years, perhaps longer for males. The greatest thing about this species is its personality. Quoting Packard and Hochberg from "Skin patterning in Octopus" "O. rubescens, the smallest species studied on this coast, is also the most vivid and varied in its displays." This was being compared with Bimacs, GPOs and O. californicus. This has been true in my own experience as well. On a more subjective note, this species seems to have more "personaility" than others that I have worked with. Perhaps this is why when Mather and Anderson decided to explore the possibility of individual personalities in octopuses chose this species (Mather, J. A. and Anderson, R. C. (1993). Personalities of Octopuses (Octopus rubescens). Journal of Comparative Psychology 107, 336-340.).
O. rubescens also seems to be an unpicky and voracious eater, readily taking frozen foods very quickly. I have fed my Manila clams, purple varnish clams, hemigrapsus, nucella and other marine snails, raw scallop medallions, feeder goldfish (good as occasional snack, and seems to be entertaining for the octopus to chase, in fact I have one octopus that will catch the goldfish, bring it to its mouth, only to what seems purposely, let the thing go again and catch it all over again), frozen raw prawns, all of which they eat readily. (the Hemigrapsus and clams are the staple of their diet, the rest are more occasional).
In summation let me just give a personal testament. In my undergrad years, I worked with GPOs, and they were my first octopus love. When begining my Masters of Biology, my committee in all of their wisdom, decided I should really do my work with a slightly more managable species, hence, dissappointedly, I picked up O. rubescens instead. I am no longer dissappointed at all. I have competely fell in love with this species and all the character that they have, and I honestly think you will to.
A caution, Like Neogonodactylus said, with all that personality, they are a bit bitey at times, and their bite can be very nasty for some people, while others have no reaction at all. I have handled this species on a daily basis for the last year and have yet to be bitten, so I have no personal experience.
Good luck and let me know how it goes.