You can't just throw a bunch of plants into a tank. The tank needs to be set up for healthy plants, otherwise the plants will die and decay and cause more issues.
You could try some java moss, which will grow under a normal fluorescent strip. It's supposed to be really hardy and easy, grows like a weed, but I can't keep it alive no matter what
Java fern is also really easy to grow and needs little light. Don't just get random plants because some aren't even aquatic even though they're sold as such, and they'll die when submerged permanently.
Not sure about nitra-zorb, since I've never heard of it. The best way to eliminate nitrates is just to do water changes. You can test them and do water changes to keep them below 40.
Hmmm, I just looked it up and not sure I'd use that nitra-zorb. It absorbs not only nitrates, but nitrites and ammonia, so if it runs out you're going to have an ammonia spike. If you already have an established filter you don't need anything like that.
A 55g tank would probably be ok, but a 75g would be better because it's bigger front to back and has a bit more water volume. If you do upgrade, do not discard your filtration system since it already has all of your biological bacteria (the stuff that removes nitrites and ammonia) just move it to the new tank.
Really you need to be tested your water for nitrite, ammonia and nitrate, probably weekly. Your water quality may not be as bad as you think, or it may be worse, but you don't know unless you test. If you can't afford a test kit, most fish stores will test your water for you.