Pushing onself too much? Is there a thing of pushing oneself too much to practice and doing too much which will cause someone to quit take a break for some time ?  what about too little ?  

how you determine the middle way here ?
There is a big obvious difference between doing something because you want it and enjoying the effort, VERSUS beating yourself with a stick like a horse. In one case you are working hard but you're enjoying it, you doing what you believe in, you're getting deep sense of satisfaction from it. In the other case, you are forcing yourself, breaking yourself, torturing yourself - you don't really believe in it, you hate yourself for doing it, but you're still doing it.

My teacher said that the feeling of special enjoyment or satisfaction is a key criteria for success in spiritual practice. If you're doing too little, you will not be happy with yourself. If you are pushing yourself too hard, you will not be happy with yourself. If you are doing it right, it may be hard and painful - but you will feel happy and proud and inspired.