Welcome to TONMO!
As the others said, the information in the articles and forums on this website is priceless and there is plenty to read that will answer most of your questions. The book also mentioned is extremely valuable to a potential ceph-keeper.
Most important is being able to first maintain a saltwater tank. The tank is like an animal all its own and you will need to know how to maintain it and keep your water parameters balanced. After that, the hardest thing will be feeding the animal you get. Sometimes they decide they just won't eat dead stuff and you'll have a hefty bill on your hands if that's the case.
O. hummelincki, O. briareus, Abdopus aculeatus, and apparently an O. macropus complex species seem to be the most commonly available in the USA right now. Avoid anything labeled or described as "Rare".
Take your time. Patience is the biggest part of this hobby. Good luck! And welcome to your new addiction.