Alright you 3, back on topic here.
20 gallon long is 20 gallon, not 29. There are many tanks that can fit the footprint of a 20 long so check out your opitons. One thing to remember is the taller the tank the higher the light needs. I don't know where to find them but you may be able to find a tank that is the same length as a 20 long but is a lot wider. This would give you a lot more options when it comes to aquascaping.
If money is not a factor and you want the fastest and best plant growth then go big. Pressurized CO2, high light and Eco Complete for substrate.
Pop in to the plant section and we will help you out there.
The main thing is keep asking questions and make sure you get what you want. It will make a big difference in the long run and you will WANT to keep up the tank instead of just feel you have to.
There are tons of options for a 20 gallon tank as far as fish. Cories, Rasboras, Tetras, Rams, some Cichlids, Danios, Live bearers, and so many other options.
If you want a fish that is one that oyu can really get into taking care of maybe a Bichir tank would be your cup of tea. They can be taught to eat right out of your fingers so you could actually interact with them like the other animals you have. I don't know enough about them to suggest which ones but someone can help if you think they might be an option. Just post a question in the ancient fish section. http://www.fishforum.com/viewforum.php?f=63