It's way too much. Here are some links that will help you if you're willing to take the time to read them:
http://www.wetwebmedia.com/ca/volume_5/volume_5_3/first_steps.htm
http://www.wetwebmedia.com/marineSetUp.htm
http://www.wetwebmedia.com/marsetupii.htm
http://www.wetwebmedia.com/smmarsystksfaqs.htm
And any of the linked pages you find above the titles on the above-linked pages will offer tons of information.
Some more info:
Smaller systems are harder to maintain than larger systems. This has to do with the dilution of waste, as well as the difficulty in keeping specific gravity constant in such a small system.
I'd also like to recommend "The Conscientious Marine Aquarist" by Bob Fenner as one of the best, most inclusive, easy-to-read books out there for the beginning saltwater hobbyist.
In this size system, the damsel would likely kill anything else. Some damsels grow very large. Try reading here and those linked files above the title for more information on damsels:
http://www.wetwebmedia.com/damsels.htm
This isn't enough room for the clown. I've got one in my 180 reef that is three inches long and eats like a pig. Again, it's not just about room to swim, it's about the dilution of waste in a closed system. The waste products don't go anywhere, so they build up more quickly in a smaller system than a larger one. Imagine a drop of food coloring in a teaspoon of water, as opposed to half a cup of water. The teaspoon will be colored much more darkly -- the food coloring is representing waste here, and it's in a much higher concentration in the smaller volume of water.
The seahorse will die in this system for reasons explained in the link I'll include here. They are very difficult animals to care for properly, especially when kept in non-species specific tanks:
http://www.monsterfishkeepers.com/forums/showthread.php?t=156078
It is likely that the urchin would die, as well, due to its propensity for grazing and the fact that you can't fit enough live rock in that tank to keep it alive. Here is a link to info on them. Again, try reading through the linked files above the title of the article on this page:
http://www.wetwebmedia.com/urchins.htm
I am by no means trying to discourage you from trying a SW tank, but I think that your experience will be infinitely more positive if you first take the time to figure out what you're doing. You'll also save money this way, because you won't pay to make mistakes -- you'll know what to do the first time around!