The basics are the same as any sw critter. Good filtration, good water quality and food. The 2 biggest issues with octo are life span and escape. They don't live very long and if eels are tough to keep in a tank octopus are ninja eels lol.
A fully cycled and mature tank with rock wrk is a good...
Live rock and the macro will help house pods. Your current stock won't do too much damage to your pod population. Wrasse and draggonets really put a dent in them
I should mention the pink color on them indicates a fire worm. Same critter just a bit worse to handle. Not many fish will eat them. Bristle worms a few types of fish will eat smaller ones
Gotcha. Pellets are ok but not as the only food. Frozen foods like mysis, sprilina brine, are better options. Still only a small amount daily is needed. The seaweed is a good thing for tangs tho.