For a first timer, bigger would be better. I would go with a 20 gallon tank, and probably the long version.
While live sand and live rock are one of the best ways at getting biological filtration accomplished in a tank, there are other ways. I would probably use a power filter, such as a emperor 400 on a 20 gallon. I would also seriously consider some sort of skimmer that hangs on the back of the tank. That way the skimmer can remove a lot of the wastes from the water.
You'll probably want to do more frequent water changes, possibly as much as one per week. This is the best way to remove nitrates without the use of live rock and sand.
Other equipment needed will be heaters and powerheads. You'll need to mix up your saltwater before you add it into a tank, so'll you'll likely need 2 heaters and at least an airpump (but I find a powerhead does a better job at mixing the water)
If you don't have any live rock or sand, you'll want to add some decoration for your clowns to hide in. You may be able to find some rocks that are safe for the aquarium at your fish store. Clay pots cut in half also make good homes for clownfish.
Hope this helps.
Hope this helps
