Hey, welcome! Pentax has the advantage in that it is pretty intuitive, much more than most other brands. The K-3 is a great choice, but maybe a K-5IIs would also fit the bill and save you some money. With cameras, the lens is often the more important factor, so its good to invest. The 18-55mm is not a bad lens, but its among the weakest in the current Pentax lineup.
The best Pentax lenses have a fixed focal length (called a prime lens, it has no zoom). These will give you great image quality, AF, and low light performance. But a zoom lens has more flexibility because you can simply zoom to change the framing. A single zoom can cover the range of many prime lenses, but it probably won't be quite as good. So you need to decide what your priority is. If you are planning on doing professional wedding photography, you will probably need the DA* 55mm f1.4 or the FA 77mm limited for top-notch portraits. Or the DA 50-135mm as a high end zoom lens. But you can also take great photos with a cheaper DA 40mm XS or Tamron 17-50mm.
Feel free to use the
sample photo gallery on this forum and read the
lens reviews section to see which lenses might suit you best.
Last edited by Na Horuk; 11-24-2013 at 08:34 AM.