Hello --
Letting the aquarium settle for a while is helpful. You can add plants though, without any problems.
If you have just a single fluorescent lights running the full length of the hood, you have what is considered "poor" lighting. Don't worry, that is very common and doesn't mean you were sold a dud! Most off-the-shelf aquaria are NOT well designed for plants. If you have two tubes, you have "fairly low" lighting.
OK, if your tank comes under the "poor" lighting level, you'd best stick to non-living plants and ornaments. You will save a lot of money over the long run. Rocks can be surprisingly effective if used intelligently, to build up a big mound, for example, where fish can hide and explore. Bogwood, bamboo, and plastic plants can also be used. Plastic plants, in my opinion, only look good when used in quantity. One or two on their own always look just like plastic plants. But a thick tangle gives a much better illusion.
If you have two tubes, things get more interesting. There are a few plants adapted to shady, low-light conditions. The most reliable and easy to grow are Java fern,
Microsorium pteropus, and
Anubias barteri variety "nana". Note that both of these are
epiphytes and must never be planted in the substrate. They grow attached to rocks and wood. If you want to make life easy, buy them ready-made, where they are sold attached to nice piece of stone or bogwood. These tend to be a little more expensive than potted or loose plants, but you can virtually guarantee that they will grow, and I think are FAR better value.
Java fern is inedible and will grow steadily under most conditions;
Anubias can get damaged by plecs but otherwise is tough and hardy, though very slow growing.
Java moss,
Vesicularia dubyana, is another shade-tolerant plant. Again, this should never be planted into the gravel, and needs to encrust things like stones, wood, or coconut shells. You can often buy it ready-made, just as with the plants mentioned earlier. Between them, these three plants all have very different shapes, and give you plenty of scope for artistic landscaping. They aren't the cheapest plants, but they are the most reliable, and so if you are on a limited budget, make the best investment. Since they don't need "soil" as such, you only need enough sand or gravel to cover the glass at the bottom of the tank.
Sand is the best stuff if you want a few catfish or loaches.
Fish couldn't care less about real versus plastic plants (except maybe those that eat plants!). What fish invariably want is some shade, and with some fish, a place to perch or rest. Most fish will be perfectly happy even with substitutes like rocks and wood, just so long as they have a complex, shady habitat that lets them feel secure. Remember, most of the fishes we keep are small species that get eaten by predators like bigger fish and birds. In the wild, they always try to stay close to cover of some kind, and if you want them to be happy, you need to respect that. What you use to produce that sense of security actually doesn't matter, just like people, they're adaptable!
You don't need to "add oxygen" to the water. Nature will take care of that. Fish usually die from poor filtration long before they asphyxiate from lack of oyxgen. If you are worried, simply arrange the filter so that spout is at or slightly above the water line. The more splashing, the more oxygen will get into the water.
Cheers,
Neale
BUT, you said that you cant usually grow anything under the "poor lighting" well i just have a single strip accross the top and I have a red ludgiwa (sp) about 15 ancharious, an anuba, and a java fern and they are all growing very well! Here I will post a pic reall quick! But overall VERY WELL SAID!! hope WE all helped you 
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