It works perfectly and looks like a new phone! Wow!
I also avoided step 21 and removed the wifi cable together with the board.
Hint for camera step 18: It was glued on very well. What I did was to lift the mainboard slighty and entered with a screwdriver between camera and case. Finally I saw that the metal plate came off too which you already have in your new case. But it was then much easier to remove it after the disassembly with my fingernails. To be able to do this step you have to remove the power button but I would recommend that anyway.