Goeie more! Welcome to the forum!
Nice purchase - that's a whole lot of camera you've got there! You could get a new lens - as you're new to photography perhaps a macro or wide-angle will help you choose a "path" - i.e. Landscape, portraiture, macro-photography, sports photography etc. Or you may find yourself liking ALL types of photography! Either way, it might be wise to learn all the tricks that your camera has to offer before shelling out on another lens. The 18-200 lens is pretty versatile and should just about cover all the bases you need for the time being. If anything, I would invest in a fixed prime lens, i.e. not a zoom lens as the image quality it always a lot better (and they also tend to be a lot "faster", meaning the aperture can be set larger to capture more light with a faster shutter speed - don't worry, you'll understand why it's a good thing before long!
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Have you got yourself a decent tripod yet? I remember when I lived in Jo'burg that the skies were always full of stars, and always thought that it would make a stunning photo with the city in the background!