I have been reading a diy forum on lowering the fit. It mentions to cut the bump stopper. Could this pose a problem when returning the fit to stock?

 

That is just a rubber piece that keeps the car from completely bottoming out. What you will be doing will make it less important. Online they go for like $11. If you're replacing the springs the hardest part will be taking off the cowell and getting at the top front strut nuts. You will need a spring compression tool for the front springs. In the states we can "borrow" them from autozone. For the back I would recommend having an extra jack to slowly lower and release the springs.