Morbo, why do you want a grip? The consumer cameras (KS2) are quite wonderful. Two batteries lasts a hard day of shooting. If you're not moving at the pace of a professional (wedding) photographer, you have plenty of time to change batteries. I got cheap ones from Amazon, and I've never had to dip in to my third battery.
The KS2 has wifi support, so you can upload images to your phone, and it has a flippy screen, which I frequently use for low-perspective shots. I bought it over the K3 as a mater of preference. If you think you might need a magnesium body, though, the K3 is the way to go. I haven't bumped or scraped my KS2 yet, and I try to carry it everywhere with me.
As to your lens dilemma, the Sigma 10-20 is a fine choice, but I'd really rather have the DA15mm Limited. Smaller, lighter, amazing. Look here for samples:
Mind Control