You already received some advice. Let me add some comments based upon my own experience.
* You already have some SLR photographic experience. The K-x and K-r are both very good entry dSLRs. But I think that you would strive for more controls and the K20D, K-7 or K-5 would suit you best.
*Between the K20D, K-7, and K-5, the final decision will be linked with your budget. If you do not have any limit, go for the K-5. Alternately the K-7 is excellent value for money right now. The K20D is another alternative.
The main advantage of the K-5 over the K-7 is the high-ISO performances. If you do not need it, then stick to the K-7.
*For the PP software, you definitely need one. Why don't you start with Pentax Digital Camera Utility (PDCU) that comes free with the Pentax dSLR? There are more user-friendly softwares, but PDCU gives some excellent results.
*For the lenses, it all depend upon your style and preference. I would however advise you to go for quality lenses. A lens is an investment, it will not loose its value and you can continue to use it in a few years when you upgrade your camera.
- If you like an all-around lens, skip the kit lenses and go for the 18-135mm, although the DA18-250mm and Tamron 18-250mm would be also an excellent choice.
- I have a DA18-250mm and a few primes with my K-7 and I shoot mostly outdoor. I shoot mostly the DA18-250mm for 80% of my photographs. The flexibility of the lens is fantastic.
Hope that the comments will help ...