Wow... not to preach but you really should have asked those questions before you had one ordered.
Since it's innevitable though let me point you in the right direction...
www.tonmo.com
Caribbean Octopus is like saying I have a Crayon coming. What color crayon? I don't know, it's a Crayon. There are several potential species coming from the Caribbean. Most likely would be Octopus briareus, Octopus vulgaris, Octopus hummellincki/Octopus filosus, or Octopus mercatoris maybe joubini, but no guarantee.
Now, while it could potentially be an O. vulgaris, you will need AT LEAST a 120 gallon tank if you plan on keeping it more than 6 months.
If it's O. hummellincki it will only grow to about 15 inches long (arm tip to arm tip) , If it's O. briareus it will grow to about 30 inches long (arm tip to arm tip), and if it's O. mercatoris, it will grow to about 3 inches long...
The hardest to ID of those would be O. vulgaris as they have a very large variety of textures and color patterns and no distinct markings. O. hummellincki has eyespots that flash blue, and look much like the eyespots you would see on an O. bimaculatus/bimaculoides. O. briareus has a distinct blue/green coloration, sometimes mottled red or white. O. mercatoris is very petite and usually a reddish brown color, sometimes with raised white spots.
A good place to buy live food is
www.aquaculturestore.com cheap fidder crabs and shore shrimp. Do not feed your octopus crayfish or any other freshwater items.
Ink is toxic but if you have a good skimmer and carbon filtration it shouldn't be a problem. It can usually be gathered in a fine-mesh net or pantyhose if you syphon it out. Potentially it is a suffocation hazard for the octopus if not removed ASAP.
The only octos that are deadly to people are the group of Blue Rings, and those don't come from the Caribbean. However, it is always possible you could be allergic to the toxin in their saliva or get a bacterial infection from the water so be careful when/if you handle an octopus.
No octopus will live more than 2 years, and most likely only a year or so in captivity. Sometimes they are already old and only live a few days/weeks after arrival.
Good luck.