Octopus Information

I'm looking to buy a live Octopus for my reef tank aquarium.

I have a tank set up to house an Octopus already. What other recommendations would you suggest?

The reef Octopus would be the best. They come as large as the size of a hand.
Some people like the baby ones which are easier to handle.
It's like having a pet because of their intelligence and abilities.
The more grown the get  the more they can be a hand full because they become smarter as the get older. Like a misbehaved child they have mind of their own which makes them endearing but they do need an experienced human to guide them and keep them safe.
I don't know how familiar you are with octopus but you definitely need a some type of closure/ lid on the tank at all times. Something that latches down like a reptile tank screen top. Octopus will explore the tank and then when they realize that they are captive, they start working ways of getting out of the tank. Sometimes if they don't find a larger body of water around they might crawl back into the tank by themselves but they can also get lost in your living room.
I want to try keeping an octopus.
What kind of aquarium set up do I need?
What is the best way to feed the new octopus?
You need a well cycled and healed tank. 1 month to cycle and then a second month to heal the tank and develop the bacteria and water parameters.
Octopus are very adaptive to habitat so you can use just about anything for decoration. You need a lid on the tank with absolutely no holes anywhere. They are smart enough to find any way to get out of the tank in a short time.
Octopus are aware that you are trying to keep them in the aquarium and understand that they are in an enclosed container.
One way is a lid made out of screen material that latches on the rim of the tank that reptile people use for their snake and lizard tanks. Octos can easily push up on a loose lid and get out that way.
You can also weight it down with something heavy.
They love sponges, craggy  rocks and live macro algae sea weed.
They do need healthy water quality.
Best food for Octopus is our live grass shrimp for the baby octo.
Once it becomes familiar with your sent and the way you look and it starts warming up to you.
Then you can slowly teach the octopus to eat non live meaty foods such as frozen silver sides or clams to supplement live feedings.
Octopus are a predator. Their not picky on any particular kind of food.
In the wild Octopus hunt and  eat live snails, clams, hermit crabs and regular crabs and small fish.
So they can be taught to eat frozen clams, things like canned anchovies at the supermarket can work, to supplement live feedings. You can get cans of whole small fish like sardines and clams oysters etc.  in the specialty isle.