as long as you enjoy the color of the bulb you have, don't bother changing it ... unlike conventional screw in light bulbs, which are different wattages but the same size, fluorescent bulbs of the same size are the same wattage, so all 18 inch standard bulbs are 15 watts, and therefore the same "brightness"
the difference in price between bulbs of the same size is due mostly to marketing, and some science having to do with the way the bulb produces it's light as well as the color temperature of the light. For example, a $5 18" bulb from home depot and a $20 18" bulb from the pet store are the same brightness and the same wattage, although your eye might think one is brighter than the other, and the more expensive bulb will have a different color
lighting is a very overwhelming market for aquaria, and there is a HUGE alphabet soup of acronyms out there. look through our
DIY forum - there is a lot of information on lighting contained in there.
as for your gravel ... 2" is not enough to really grow heavily rooted plants, however, you can always grow your plants in pots, when you are ready, you can go to walmart and some smallish terracota pots (like 2" across) and a bag of Schultz Aquatic Potting Soil. just rinse the soil, add to your pot and plant something in it, after a few weeks the plant will establish itself and should start to grow for you!