They're not as hard to keep as you think.
I have a bimac in a 55g tank. He's very small right now, but may outgrow the tank in time. In fact, I expect him to.
There are some great web articles on keeping octos. I used many of them as resources as well as a friend who conducted research on them in Tampa.
If they haven't mated, they're success rate is considerably higher...
Mine's eating like a hog and doing well so far.
And they are very cool to watch.
Yes, seal up the tank if you get one. Avoid the blue ring unless you want to risk dying for your pet.