You already received some very valuable inputs. It all depends upon your budget and your needs. I went a different path from other suggestions. Let me share a different experience
I purchased the K-7 body together with the DA18-250m, and shortly after the Voigtlander Nokton 58mm 1.4. That is, an all-around zoom lens AF, and a fast prime MF. I love the combo of two complementary lenses, and I would do it again.
I like to work with a simple system (1 lens and 1 body) to travel light with a small bag and avoid lens swaping. My basic setup is the 18-250mm that is an excellent all-around lens, well-regarded by Pentaxians. I shot outdoor incl. actions (waves, birds, surfers, storms). I do not want to change lenses, especially when the weather conditions are poor, and the DA 18-250mm is perfect. Let keep it simple!
I purchased the Nokton 58mm for low light outdoor photography. As a fast prime (f1.4), it has a large aperture. Again, when I take it, I do not change lens when outdoor. I found the Nokton to be a superb lens both indoor and outdoor, and I use it much more than initialy thought.
Overall I am very happy of my setup that suits perfectly my needs. Both lenses are very solid and sturdy. They are not WR but their built is superb.
Hope that the comment may help....