I didn't want to wait either to put something in the tank, so after 2 weeks (the tank still needs to cycle some) I added some damsels. Then every week after I added a fish. Apparently I went too fast because they all died. I think they got some kind of disease and I was told to get a QT tank for them, but didn't go fast enough and they all died.
Damsels are hard to catch. I got a very aggressive one that was picking on stuff 3 times his size so I took him out. after several hours of trying to net him, and even trying a fish trap (DIY), I finally ended up having to take out all the rocks. Well after all but one of the rocks were out the retarded fish instead of swimming around decided to swim into a hole in it, so I took that rock out and shook out the fish. I punished him by leaving him out of water for a few minutes while I put my rocks back and making him live in a little cup for 12 hours until I could return him to the fish store. He was bought by someone 10 minutes after I traded him in (he was a pretty fish).
So if you get something to look at make it something slow and easy to catch, which is quite limiting. Or just get something cheap and non-aggressive that your octopus can eat.
A clean up crew is a good idea after 3 or 4 weeks. They aren't very interesting, but the snails are fun to watch the first few days you have them if you've never had them before. When I got snails, my family watched them eat on the glass instead of the new fish. You should wait on starfish too and not add them until around the same time you add your ceph. They are sensitive and die easily. Around 3 months is when pH becomes more stable, so that is a better time to add starfish.