I owned a tropical fish store for three years. Then I started a business taking care of peoples tanks in their homes and offices. Here are the key points: Start with a big tank - the bigger the tank, the slower the chemical fluxuations take place. get a good (easy to read) book that teaches you about the chemical balances of your water (specifically your nitrate cycle). Generally, it's the very same as fresh water, but everything is a lot more expensive. When you make a mistake with salt water, it costs 10 times as much as the same mistake with fresh. I would be happy to help anytime you have a specific question, and, no, it's not hard. I love cow fish too. and dog face puffers. and mandarin gobies. Cow fish, however, are poisionous to your other fish and your water when they die, so dont start with those :) Get your water cycled first.
Here's my tips: Get a big tank, dont skimp on the filtration, and start with lots of "dirty" water (you can get at the pet store) and "live sand". Start with Damsel fish as they are hardy enough to make it through the origional cycle and not too expensive.
Look for a used tank online (Craig's list or something) to save $ but genarally you can get a good big tank and filters for under $10 per gallon. Price goes down (per gallon) as size goes up. DO NOt start smaller than 55 gals (and that's pretty small).