The creeping forward bit is in extreme cases usually.

The biting point being low down is another dead give away. You noticed any clicking noises from the pedal or the biting point constantly changing when you are driving?

The gearbox will crunch in reverse as they dont have a synchro mesh, its a direct meshing of the gears. Usually u need to hold the clutch in for a few seconds before selecting reverse to allow the gears to stop spinning, but if it still crunches then that shows the clutch is still turning the main shaft in the box.

I bet you.....a jam tart, its the quadrant gone, and to answer the question aswell, the cable isn't adjustable, thats the quadrants job. Everytime u push the clutch and then return it to rest the quadrant pulls the slack out of the cable to compensate for cable stretch and clutch wear.

So, you will be relieved to know the quadrant is very cheap to replace, while also being that its a slag to fit