As long as they fit, you can use any tube with any lens.
To take your 50 mm lens to 1:1, you need a total of 50 mm in extension. Some of that is provided by the lens (thefocussing extension in the mount), the rest will need to come from the tube(s). (Or you could leave the lens set to infinity and add 50 mm worth of extension tube(s). But mind that with FLE lenses, you have to set the lens to its close focus limit - and then add whatever you still need in extension using tubes - to keep image quality as high as possible.)
As far as shifting the focus point is concerned, tubes and bellows work just like the focussing mount: the more the lens is moved away from the film, the nearer the point it is focussed on.
There's a simple relation between image scale and extension: total extension / focal length = magnification = 1/scale. ("total extension" includes whatever the lens itself brings along in its focussing mount, if the lens is not left to the "infinity" setting).
So add 25 mm worth of extension using a 50 mm lens, and the magnification will be 0.5x, scale 1:2. Add 150 mm and magnification will be 3x, scale 3:1.
So how much to use with any lens to get to, say, 1:1 depends on the focal length of the lens.
If the tubes are not-automatic, i.e. don't link the aperture mechanism to the camera, you need to stop the lens down manually for metering and taking pictures. Though some non-auto tubes do that for you, stopping the lens down to the preset aperture permanently, and you will have to set the lens to its max. aperture for focussing.
The bellows unit will - with almost 100% certainty - not be automatic, so the same applies.
All it does is add even more extension between lens and camera, extending the focussing range into 'the near' even more.
If you don't have one already, you will need to find a M42 to Pentax mount adapter ring to put the lens on the bellows.
