Since you already have an M9, you might prefer your DSLR setup to have maximum differentiation from your rangefinder setup. As you already know, the advantages of the M9 is in its access to Leica glass, its small size, its quiet shutter, its full frame sensor, and in the silky smooth workflow. The disadvantages of the M9 are in its lack of autofocus, plus its general inability to use zooms, macros, or long telephotos.
(The K-5iis also has a technically superior sensor, with emphasis on the word "technically". I don't like pixel peeping or placing too much stock in DxOMark, especially when we're comparing apples to oranges, but the K-5iis does have better high ISO performance, especially when it comes to dynamic range.)
Looking at it that way, let's think about what lenses would best take advantage of the Pentax K-5iis, especially as compared with the M9.
The 21mm is great if you'd like your K-5iis to have a quasi-rangefinder feel. It's a tiny, sharp lens with excellent, trademark Pentax colors. It's a slow-ish lens, but it's sharp wide open, and you can use the Pentax at higher ISOs than you can your M9.
As for your walkaround zoom: if you don't need weather sealing, then I would strongly urge you to consider the Sigma 17-50. The IQ truly is top notch - tack sharp in the center wide open, prime sharp when stopped down. Smooth bokeh and gentle Sigma colors. I have found the AF to be quiet and reliable. You may have to spend a few minutes doing AF fine tuning to get the lens just right, but once it's done, it's done. The build quality on the Sigma is more than good enough for real world use.
I've heard too many mixed reports about the Pentax 16-50 to spend any time or money on one. I've tested a few out, but the AF always felt poky. What's more, nobody seems to think that the Pentax 16-50 is nearly as sharp wide open as its competitors from Tamron and Sigma. The Pentax costs much more than the Sigma and the Tamron, so if you don't need that weather sealing, then you're really only paying for the name.
It's sort of funny, to think that you could wind up with Leica lenses for your M9 and Sigma lenses for your Pentax, but hey, whatever works.
FWIW, for my WR lenses, I use a Pentax 18-135 WR (and a Pentax 100 Macro WR). The 18-135 is slower than the 16-50, of course, but it's reliable, it's durable, it has a wider range, it will never have SDM failure, and what's more, the image quality is actually quite good for its price and capabilities. There's no point in quibbling over corner sharpness if using the 18-135 means that I actually get the shot, as opposed to missing out because I was using something "nicer", but less flexible, especially if the 16-50 is going to be scarcely any better at f4 or f5.6. I can carry one in my backpack and not worry if it gets wet or banged around.
As for other lenses to get, it might seem a bit obvious, but people love the Limiteds. They're all good. Find a focal length you like and just get one. The 31mm is a logical choice for a fast, premium normal lens. The 35mm Macro is a weird idea, but there's a lot to be said for weird ideas, especially since you can't do macro on a rangefinder. People have fun with the 15mm, especially since it's so tiny, but it might be weird to have both the 8-16 and a 15mm prime.
I used to have the 70mm, and while on the one hand it had some of the best IQ that I've ever seen in a lens, I also didn't take nearly enough portraits for it to be worth my while. The lack of close focussing didn't help, either. That said, the idea of a high-quality pancake telephoto is actually pretty cool - it'd be great for event photography.
