Was curious to see just how much light it takes to do the focusing so set up in the basement, some daylight coming in, on a very dull day. Focused on the upper unpainted hinge at f3.5 without any difficulty. Light level was such that the exposure was ISO 100, f 11 and 20 seconds exposure.
I know from experience that the vast majority (98+%) of the images I make are at less than 30 seconds so I conclude that focusing will not be a deal breaker.
I just tried focusing at f11 (a lot less light - actually less than 1/8 as much light) and the screen goes a little grainy but not bad, and focusing even with the greater depth of field and slow cycling of the image, and the noise was not a problem. I used a magnifying glass on the magnified image and that really didn't work at this low level and large depth of field. I opened the lens again to 3.5 and retried focusing the magnified image with my magnifying glass in hand - and that worked fine and felt more secure than without the magnifying glass - slightly noisy screen notwithstanding.
Bottom line: I don't think manual focusing will be an issue under 30 seconds, f4 for the focusing and ISO 100. No idea what it would be like for photographing star trails - not something I've ever done.
OF course, the image recorded isn't noisy, just the screen and viewfinder, and only under this low light.
Can't tell about autofocus as none of my lenses are autofocus on the adapter anyway and even those that are for the Pentax, are almost always focused manually in the kind of work I do.
I hope that the 32-64 lens turns out to be sharp, and that in a year or so they will add something like a 64-128, and a 128-256 or thereabouts high quality zooms. Pentax has an old 80-160 which is reputed to be very good, and a 150-300 which isn't, more's the pity as on full frame, my 70-200 is my most used lens.