My first reef tank was a 20 gallon, that was more than 20 years ago. I made a few mistakes, but it did quite well. It took about 6 weeks to cycle, but I did not have access to live sand or much live rock at the time. I used crushed coral, a little red lava rock, and tufa rock at the time. I also had an UG filter. I would not go any smaller than a 20 gallon tank to learn from, bigger would be better, but it is a good start.
Things have changed alot since then. I would recommend no UG filter, a deep sand bed, approx 1.5 - 2 lbs of live rock. Good lighting would be of great benefit for your tank. Power Compacts or good VHO lighting would work well on a 20 gallon tank. Read all you can. Books are good, but so is this forum, there are many knowledgeable people here, you can learn from their mistakes.
Remember that you local fish store may not be the best place to ask questions, they are usually interested in moving merchandise. Post your questions and someone will give you answers. You can also search old posts on the forum for more information. Do not be too impatient, it can cause more problems than waiting.
Welcome to the wonderful world of reefing, it can provide many hours of enjoyment. If done slowly and properly, you will be successful and contributing like the rest of us.
