The only experience I have with aquariums is the fish I got from Walmart as a kid. I have no experience whatsoever.
Okay. I will condense a lot of info in to what you could do. First and foremost you need to learn about the nitrogen cycle in a marine aqaurium. If you haven't already.
Live rock plays into learning about the nitrogen cycle but I want to inform you of something.
People might tell you that you need X amount of live rock per gallon in your tank... while it does not hurt to run a tank with a lot of rock. It is not completely necessary. Look up minimalist marine aqauriums and you will see what I mean. Octopus do need hiding places though. So keep that in mind as well. Just make sure the filtration you use can hold a lot of bio media to compensate for less "in tank" rock surface. If you use a basic HOB filter of appropriate size then more live rock is necessary. Do a little research and then go from there.
As far as tank set up. If your looking to stay in the cheaper end. Cheaper is more complicated in my opinion. But it can be done. Get yourself a size 40 breeder tank. You can get away with putting a bimac in there. Though bigger is better. It is not really necessary In My experience. My bimac got good size, but she still would of been fine in a 40.
Research filtration. What brands and types. Get a high overturn rate. I use a canister filter. If you have a roughly 40 gallon tank, get filtration with a flow rate of 160 GPH minimum. More is better. But you don't want your aquarium to be to turbulent either. Power heads are good for flow but you might have to cover them in mesh if they have gaps big enough for octopus arms to fit in. You need a protein skimmer. Dwarf species you can get away without a skimmer. Everything else you would need one from my understanding. You can reaserch what size skimmer you need for what tank.
Octopus do not need special lightning. So you can go cheaper in that end.
Octopus are pretty easy to keep. Don't let people scare you. They are pretty hardy.
Look up 'Advances in laboratory culture of octopus for biomedical research' by Hanlon and Forsythe. It gives you some parameters in there.
You will learn they are actually pretty tough little buggers.
Temperature is important for octopus as it can slow or speed up there life cycle. So try to keep octopus on there low end of their Temperature tolerance if possible. That is up to you though. If you want a short term pet that goes through its life cycle quickly then higher temps work. If you want to have one for longer, lower the temperature.
