Well it all depeneds. Are you looking to set up a Reef or Just a FOWLR (Fish Only with Live Rock) tank? If you are looking to do a FOWLR set up, it will be lest challenging and less money. A reef would require a light that can grow corals while a FOWLR set-up would not. And as of the clownfish, you might not want to get one. They prefer a larger aquarium (20 gal) but many people keep them and when they get too big exchange them at their LFS.
So, where to begin. If you want to do a reef, I would recomend visiting this web site
http://www.nano-reef.com/ it has a lot of great articles on keeping nano-reefs.
Also, make sure you do plenty of research. Starting off you will make mistakes and knowing how to fix them is where your reaserch will really come in handy. The internet is a great tool.
Any other questions, dont hesitate to ask.
There is a lot of great info here