Thank you for coming to the forums and WELCOME! I hope you enjoy your stay.
I would not use a canister filter on a saltwater tank. I know some people have in the past with success, but it's hard for beginners. Too much cleaning and then things could go wrong. So, I would start with a simple Emperor 400 biowheel filter. It has two extra filter baskets for different media. Also, the filter cartridges aren't extremely expensive. It's a very good investment for a novice to amateur aquarist.
A protein skimmer isn't absolutely necessary at the beginning, but it is necessary to save up for one. Avoid at any cost Seaclone protein skimmers. That's another mistake because you see the price tag and think a skimmer is a skimmer - but avoid it at all cost. It doesn't work and is not worth anything unless you modify it a whole lot. I would suggest a coralife super skimmer - it's great value for the price. If you are going to buy a skimmer, I would suggest going double the aquarium volume, regardless of what the skimmer says, unless it's octopus, deltec, bubbleking, or tunze. There's a couple others out there.
For rock, you should at least buy 1 to 1 1/2 pounds of live rock per gallon, or until you have the aquascape that you prefer. Also, 1 1/2" to 2" of sand on the bottom. You don't have to buy all live sand, and infact, if you can, get a scoop of sand out of another persons tank and add it to yours. That's the best way to start off a live sand bed.
If you are just planning to have a fish only with live rock tank, I wouldn't invest a whole lot of money into lights. Save up some money and do a lot of research to find what type of lights will work for your tank if you are wanting to buy corals or expect coralline algae to grow.
Good luck and we're all here to answer any questions.