2 filters better than 1?

I personally would not do an underground filter. Now I used to be big into them and have had them blow up on me and kill off all my fish, and I was maintaining the UGF as recomended. I am glad you read the 1 inch of fish per gallon myth and yes you can get more fish, but unless you are going to do a fishless cycle you should add your fish slow.

As for other filtration a bio-wheel is a great thing, and having a second filter is not a bad thing to do. Your tank is smaller so you can decide what you want to do, but a few options are a canister filter with a bio-wheel. If you want to save a few bucks get one used either on craigs list, e-bay, or local papers. You can go with a HOB (hang on back) filter with a bio-wheel, or you can get one of the small internal filters and they usually have a sponge in them.

For the light I am going to assume that you have plastic plants since it was a kit. The light is said to be for viewing only, but I have notticed that when I did that and I would go for a day or two with out turning the light on my fish would lose their color (which equals stress). I have also read that it is a good thing to have the light on 10-12 hours a day. I have my florecent light on a timer for 10 hours and my fish have been healthy.

Fish being pale or mottled is not necessarily stress, in the case of lights-off, it is adaptation to the current conditions.

Opting for more than one filter system is a personal choice item. Many of us use redundant systems as insurance and a safety factor. All of my tanks are multifiltered.

HOBs, canisters, W/Ds, UG/RFUG, etc. are all perfectly acceptable filter formats. Each has its own requirements for upkeep. The choice is again in part personal, in part the needs of the particualr fish to be housed. But over-filtration does not in itself allow overstocking. Extra filtration makes upkeep easier and safer, but it des not change the capacity of the system.

A second filter would be ok, but if you really want to be able to keep more fish get some live plants. You don't need to fill your whole tank with plants, one or two for know would be fine and would really help support more fish. Java ferns and Anubius plants are really hardy if your just starting off. I know some one with a 29 gallon planted tank and he has 30 fish in there! Also, if you want to keep tetras make sure your tank is set up exactly right or get ready to spend a lot of money, because tetras are very, I repeat very fragile fish, especially the neons. A good alternitive, if your not really stuck on tetras, is to get white clouds. They are a schooling fish and look a lot like tetras as far as body shape, and are very hardy. Make sure you read the sticky on cycling your tank before you add your final inhabitants. Good luck, and welcome to the hobby.

Oh, one more thing. check out www.liveaquaria.com lots of good info of different fish there.

I'm pretty sure it's okay to poke your hands around in the tank. I'm allowed to pat the koi at my LFS, which amuses me to no end.

Yes you can put your hands in the tank, just wash your hands before (not using soap) and wash your hands after with soap.

yes you can just plant the plants in the gravel, and you can just attach java ferns to rocks or driftwood if you want. And don't worry about putting your hands in the tank I do it all the time when I have to net fish or do regular water changes or fix my plant, you get the idea just make sure your hands aren't really dirty or covered in some forein chemicals or something.