Hey, welcome! I'm not quite sure what your questions are. Maybe if you post photos (scaled down to max 800 on long side) with exif data in tact and labelled what settings you used, and which lens. These photos should be done in daylight, with a relatively near subject, hopefully using 2sec timer and a tripod/base.
But on to manual lenses. There are some different types of K-mount lenses. I'll explain quickly:
1) Fully manual, preset. I think the Mitakon K-mount lenses are like this. The mount fits on K-mount without needing an adapter, but they have no coupling, no levers, digital contacts, nothing. You simply use Av mode, focus with the lens wide open, then move the aperture to the number that you want, wait for Av mode to re-meter and set the shutter speed (and ISO, if auto-ISO) and take the shot. When you choose aperture, you immediately see viewfinder darkening, DoF widening.
2) Almost fully manual, but has aperture lever. The M series fits this description, like your M 50mm f1.7 (love that lens, btw). Here, the camera doesn't actually know what the chosen aperture is, because the lens has no digital contacts. But the camera can move the aperture from wide open to the one you selected on the aperture ring. The lens aperture is kept wide open for focusing, and gets stopped down when you press the shutter speed - but only if you have M mode selected. Choosing Auto-ISO or any mode other than M will default to Av. Av mode with manual lenses has the advantage of constantly metering and adjusting shutter speed (and possibly ISO), but it always keeps the aperture wide open, ignoring what you selected. You can use green button to have the camera stop down the lens to your selected aperture and set the shutter speed.
3) A-series. These lenses have no AF, but they have A on the aperture ring (you need to press a little button to select it, but then you just leave it there). Here the camera actually knows the aperture, and you can choose aperture on the camera. These lenses don't have in-camera lens corrections or AF, but they allow P and other modes.
4) Fully automatic. These lenses have lens ID, A-mode, etc.
I hope this sheds some light on what the camera is doing. With the M lens, you need to use M mode if you want the camera to choose any aperture other than wide open. Av mode and Auto-ISO can be used if you want to shoot wide open.
This is why different lenses might or might not darken the viewfinder depending on the choice on the aperture ring. And this is why sometimes the camera will ignore your aperture ring, and other times the aperture ring setting will only show up in the photo, and other times it will show up in the viewfinder.
Live view is a little special, because the camera will try to keep it a certain brightness to help you compose and focus, even if the scene and photo will actually be darker.
Regarding metering, I think with manual lenses, the camera can only use spot metering or center weighted.
Maybe you can refresh your manual lens skills with this tutorial:
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html