If you're looking for a body that has an optical viewfinder, the k5ii or k5iis has been by far the most reliable. I've had my k5iis for almost a couple years now and it's been great. That said, I've heard of some users having issues with the k3, but I did not feel that the problem was widespread enough nor debilitating enough (just remove the battery to stop the cycle) to warrant avoiding the camera so I've recently bought the k3.
Regarding your question about lens choice... I assume since you've been using Canon gear, your aware of crop factors and have calculated that into your request. So... the FA31 is a pretty fantastic lens, but it's pretty fantastically priced
The DA35 f2.8 macro is a great all rounder that can do pretty much everything well but since it's a macro, it's focus speed is a bit on the slow side. The DA35 2.4 is a great lens that happens to not cost that much. Another lens that has been reviewed very well has been the Sigma 30mm f1.4. If you're looking for a zoom, the Sigma 18-35 f1.8, Tamron 17-50 f2.8, Sigma 17-50 f2.8, Pentax DA*16-50, and Sigma 17-70 f2.8-4 are all great lenses. Of these, the Pentax 16-50 is the only one that has weather sealing.
In the 50mm range, the Pentax DA* 55 f1.4 is really great and is weather sealed. If WR isn't too important though, there are many good choices - DA50 1.8, FA50 1.4, DFA 50 2.8 macro, F50 1.7, and the Sigma options are all extremely good. And if manual focus is ok, the SuperTakumars are still excellent performers as are the M, k, and A series Pentax lenses.
For some ideas of the pics you'd get from these lenses, head over to the lens section of this website - there is a ton of info over there.
Good luck and congrats on the k01!