iolair
No longer a newbie, moving up!
The problem occurred with earlier serial numbers only of the K-3 II, and has been fixed for free by Ricoh. It never affected the K-3. (Some earlier K-3 models had a flappy mirror problem, but that only affected a tiny proportion of users and was fixed by a firmware update).Ricoh had to recall a lot of the Pentax K-3 II models, because they had some issue when turning the camera off—parts of it would stay on until the battery was removed. The K-3 is so similar, that it would simply be a safer bet to go with the tried-and-true camera.
Pentax have a very long history and easily a big enough customer base that they are definitely "tried and true".
As you point out, while the K-3 II has built in GPS for the astrotracer function, this can be added to the K-3 via a pricey add-on module. Also, in the interests of fairness I should point out a significant disadvantage of using the astrotracer function: it will add motion blur to any ground-based elements within your scene. (Of course, even on the K-3 II you can ignore the astrotracer and just go for standard long exposures).
Another issue when looking at your budget of money and hiking weight is that for astro shots, you should factor in a good quality tripod too.
Personally, I see that all the major manufacturers (Canon, Nikon, Sony, Ricoh/Pentax, Panasonic, Fuji - and most recently Samsung) are producing bodies that easily fill the OP's requirements. However AFAIK, only Canon, Nikon and Ricoh/Pentax have a sufficiently large lens collection to cover all bases at different levels. (Sony have a good lens range, but don't really have entry-level lenses - though that's not a problem if you've got a lot of money to spend). There's a lot to be said to trying the options from different manufacturers and seeing which you feel comfortable with, too. I find there's a big difference in the usability of different manufacturer's bodies - Pentax is the easiest I've tried, Sony is very good, Canon's okay - but Nikon I find awkward and counterintuitive to use. (Obviously that could be overcome by more time to get familiar - but why bother?). This last point is very much down to an individual's user experience, so you may prefer something totally different to me when you actually go into a camera shop and have a play with the different models.
I'm afraid I've barely touched the Fuji cameras, and while I had a favourable impression I certainly don't know enough to give a meaningful comparison between them and the others.
Incidentally; and this may be a matter of personal opinion, I find the colour detail in darker areas of Canon images weak - a shortcoming of their sensors - and would avoid them for landscape work.