I have the K-3 and recommend it, especially at current prices. Although I like the versatility of the 18-135 zoom range (and when I travel I pack it and the 55-300 for a lightweight, WR and versatile system), when I'm not constrained by weight limitations, I tend to carry Sigma 17-70 plus WR 55-300 around instead. I like the extra mm in the wide angle range and the slightly faster lens.
Given that you're interested in portraiture, you might consider getting the K-3 plus 50mm combo, rather than K-3 plus 18-135 combo.
I would add to your gear list (and rank it pretty close to the top) the WR 55-300. It produces surprisingly nice images, it's small, lightweight and WR. I shoot portraits with it (when the light is good), it's great for critters (mostly what I photograph) and you can even do something interesting stuff with fauna if you're far enough away from it.
Lately, I have really enjoyed photographing with a couple of new macros I added to my kit during the fall sales: the Pentax 35mm Limited Macro f/2.8 and the Pentax FA 50mm f/2.8 macro. I photograph dogs and cats for a rescue group and with these lenses I can shoot some nice environmental portraits as well as doing some very close-up images (because of the macro capabilities).