I use the API Master Test kit. I do all my shopping here: http://www.fosterandsmithaquatics.com
they have a much better selection of items than any pet store, they offer very reasonable flat rate shipping, and their prices are easily $10-$20 lower than any pet store.
Live plants really help with the water quality much, much more than they harm it since they feed on the waste produced by the fish. It's important to have a fluorescent light, and you may also consider getting a supplement like Seachem's Flourish Comprehensive. Good low light plants include anubias, java fern, java moss, hornwort, and if you're feeling lucky, you might try some species of cryptocoryne. Be aware that many pet stores will try to sell non-aquatic plants as if they were aquatic--these plants cannot survive if they are submerged and will create a huge mess in your tank. Common culprits to watch out for are ribbon plant (lucky bamboo), purple waffle, mondo grass, brazilian sword (peace lily), bamboo, and really anything that you think might be a houseplant.
And definitely do not get any kind of algae eating fish. Plecos can grow to be exceedingly large, and even small varieties produce way too much waste to be manageable in such a small aquarium. Otoclinus are not suited for this tank either--they are extremely sensitive and seldom will eat prepared foods because they are wild caught, they are also social and need to be kept in groups. If you get any kind of algae eating tankmate, I suggest a nerite snail. They're attractive, efficient algae eaters, and they have a lot of trouble reproducing in fresh water, so they will not take over your tank.
Also, if you see a fish suffering in a pet store, it's a good idea to complain to the management. Even if they don't let you have the fish for free, they can at least euthanize it so it doesn't have to suffer anymore.