I'm new to this hobby as well. The one thing I learned...you need to have patience. Do you have any good books on SWF?
I have the New Marine Aquarium, and the Saltwater Aquarium for dummies book. The first one, takes you step by step on equipment, cycling. Actually setting up the tank. Both are very informative. I've also heard that the Concientious Marine Aquarist is good too.
In addition to your items already, you need a heater, if it's a FOWLR, a basic double strip lighting systems is all you need. preferably one bulb that's actinic.
hydrometer is necessary, Various test kits for Ammonia, Nitrites, Nitrates, Ph, etc. all of this info, you'll find here, and in those books i mentioned.
some people think you can wait on the protein skimmer, but I bought one right away. As far as the number of powerheads, I believe one would be enough for your size tank. I maybe wrong, I'm hoping someone else will add to this list.
One thing for sure, that I'm finding out for myself...this is not a cheap hobby, and it's also not for anyone that wants instant results. Good luck to you. I should be setting up mine in a week or so.
:happyfish