There's a lot of help if you use the search feature up top there. I started off just reading and reading the stuff that was there. What tank you buy is probably going to be determined by wether you're going with a dwarf or not. My first ever tank (ten years ago, mind you) was a 29 gallon, and the species was whatever the LFS happened to get in. (I think it was O. bimaculoides, but I dont have any pictures so Ill probably never know) I didn't know what I was doing and I dont think this website existed then. 29 was waaaaaaay too small though.
Some people here have had a lot of success keeping mercs in 20ish gallon setups, but they seem to be quite reclusive and shy as a species. O vulgaris, the common octopus needs tanks around 150 gallons or so, the bigger the better it seems. I'm working on collecting the equipment for a ceph tank myself right now, but am limiting myself pricewise and trying to do a lot of it by scavenging second hand materials...I havent even decided octopus or cuttlefish yet and I'm probably going to be doing a lot more research. I probably wont have things up and running for 6 months to a year...
All that being said, from one noob to another, welcome
Take a looks under the ARTICLES button at the top of the page; there are some equipment lists and care sheets that can give you the best overview. Nancy and Colin's book is also probably the best overview reference.