Octopus are arguably the coolest creatures we can keep. But they do have a few quirks that make them difficult. They will escape through any hole as large as their beak which is not that big, so a 2" octopus can get through this --------> 0 <----------
You can fix that by having a few inches of material like Velcro all around the top of the tank as they can't climb on that. They will also go into any air hoses, filters or pumps. Remember they can swim, crawl and maybe fly
The other problem is they only have a life span of maybe 2 years so if you get one a year and a half old, he will croak soon.
I feed them fiddler crabs which I can easily collect here but they will eat small fish and sometimes clam meat.
I had this one spawn in my tank. The female dies after that. I fed the babies adult brine shrimp.
They catch the shrimp and while they are wrestling them, they "ink".
Very cool.

You can see the babies here.