Looks like a great CarPC Setup!
I went over your wish list; I must admit, you did your homework!
Especially on your choice of HDMI cable; you are going to need something shielded and very-VERY long to do what you need it to.
As far as the keyboard, I recommend this unit, which not only includes it's own mouse/trackpad, but it's $8 cheaper than the bluetooth keyboard you are interested in. You'll say, "Oh, it's RF/USB" and what not, but depending on how you setup your unit, this may work a bit better!
I'm also curious as to how you plan to set up this unit in your Montana. From the looks of this stock unit, you probably can fabricate a 10.1" HDMI LED screen and set it up in front of the stock head unit! I figure $50-$75 for the screen, $40 for the LCD controller (both found on eBay), and if you can fabricate the housing yourself, you can spend up to $200 tops for a screen with suction cup that will match the Montana! It's just a thought.
Best of luck, and let us know how it goes!!