Andrew,
I have just started
SW myself. I did a HEAP of reading before I took the plunge, and it helped a lot. I am still confused on a lot of stuff, but it a learning process, and its heaps of fun. A good book to buy is
"The New Marine Aquarium" by Michael S Paletta, its a very good starting point with a heap of info on what you will need and can expect. Another book is
"The Nano-Reef Aquarium" by Chris R. Brightwell. Very good for small tanks.
I started small with a 10gal Nano, and its been good as the expense hasn't been huge to get to the stage I am with my tank (I am now building a 120gal as well). A good site for small SW tanks (Nano's) is
http://www.nano-reef.com lots of info on small tanks, and good info guides on setting up 'without' protein skimmers and sumps. Just gotta keep on top of the water changes and check you chemistry alot (mostly just
SG,
pH and KH after its cycled)
Good luck which ever way you decide to go, and I have to say I am having more fun with my new SW than I ever did with tropicals.