I concur it sounds like crushed coral.
Are planted salt water tanks normal?
I would say they are not overly normal in the fact that saltwater does not really have plants like your thinking. In saltwater you have either corals (these are animals just like fish and such) or you have algae. There are decoritive algaes that look plant like but the key to keeping them is making sure they dont go 'sexual' on you as they can polute a tank when they release their spores.
Most people who start out in the hobby are intimidated by the prospect of corals so they start with a fish only setup. Then as they get more comfortable they slowly migrate by adding other inverts to the system. You can have a fish only setup or a fish setup with live rock. The only real difference is the introduction of live rock in approx quanties of 1 - 1.5lbs per gal
. The concept with the live rock is that it acts as your biological filter. Thus you need less filter equipment with a tank that has the proper amounts of live rock.
Do you need a sump? No. No one needs a sump but sumps have their unique advantages that often make larger tanks easier to work with when they have a sump. As you describe your tank as having a little part cornered off with a hole in the bottom then yes it would proably be in your best interest to have a sump simply because your tank is pre drilled and that little corner is an overfllow. The overflow is how water gets out of the tank and into the sump. usually there is a return line also. If there is not a second hole then you will have to return your water up and over the side of the tank. Still not that big of a deal.
Saltwater and canister filters really dont go together like they do for freshwater. If anything they surve the prupose of moving water around and thats about all I would use them for. I would leave the acutal filtration up to my live rock and my sand bed.
Is there a good site for general SW tank knowledge?
Sure. Your using it right now. There are probably many websites out there that attempt to tell how to setup a tank from start to finish but the problem is there are so many 'correct' ways of doing something that it can easily become a huge debate over what method is correct vs incorrect vs a waste of money vs not enough.
I think you might find a few books to be of a good resource to you. Not because we dont want to answer your questions but bascily because with a book you can read and re read the parts of the book time and time again. Supplmenting the internet with some books is a great way to increase your knowlege and comfortlevel with the hobby.
The book The Conscientious Marine Aquarist by, Robert M. Fenner is one of books top on the list that I recommend to people starting out. Its a great reference from just the general startup and different types of saltwate aquariums as well as providing some basic information about many of the common saltwater fish we keep. Another book that coveres alot of the basic aqaurium setup is The New Marine Aquarium by, Michael S. Paletta.
Both of those books and many other saltwater reference books can be found in our saltwater library. http://www.aquariumadvice.com/saltbook.php
I have both of the books I described above and still reference them from time to time.