Your multiple long exposure issues may be due to the camera performing it's "noise reduction" cycle. Unless you disable the noise reduction features, if you've just made a 30 second exposure, the camera can then spend another 30+ seconds processing the image before becoming available for another exposure. Experimentation balancing ISO against shutter speed can reveal a "sweet spot" with no delay, but will possibly require a wide-aperture lens to be of very much use.
Focussing and screen visibility can be an issue with low light subjects and smaller-aperture lenses. I've taken to focussing on a bright subject before repositioning for the final exposure. I've also used wide-aperture wider-angle lenses to align the camera before re-fitting a pre-focussed longer-focus lens for the final exposure. Using the "Digital Preview" feature (p.138 in the user manual) can save cluttering the card with unwanted images
Moving the Mode Dial from 'Bulb' to another choice can "encourage" the camera to "re-evaluate" it's circumstances and present a brighter, if somewhat grainier image. You may need to half-press the shutter button to re-activate the meter. Don't forget to change back to your preferred settings to make the exposure.
As with many of the unfortunately poorly-documented features on our Pentax cameras, "playing about" for an hour one afternoon (with the lens cap fitted to "fool" the meter, if necessary), can save endless frustration once out in a dark place with limited time to achieve the anticipated results.
You may find some useful guidelines here
Pentax Astrotracer Guide and GPS Feature Comparison - Articles and Tips | PentaxForums.com
More good stuff here
PENTAX: The choice for astrophotography / explore | RICOH IMAGING
Lots of useful information here and the subsequent videos.
Afterthought : Set up a "User Mode" for Astrophotography and save your preferred settings there.
Inevitably, YMMV - good luck