Is it possible to use a spring which does not obey hooke's law as a force gauge? If so, how? also If you incline the plane so that the block starts to move do you expect it to slow down and stop? If so why? If not, what do you expect? How can you measure the kintetic friction coefficient using the inclined plane only?
Hooke's law is approximation that states that there is linear relationship between force and displacement. In order to measure the force through the displacement, you have to know the law with which force is related to that displacement (the extension of that spring). For example if the spring has characteristic where the force goes with the square of the displacement then the spaces in your scale wont be equal but will be getting bigger according to the square rule. So in short yes if you know the law force-displacement. If the block starts to move by its one, then it will continue to move until some obstacle stops it, assume the angle is not changing, so I wont expect it to stop.