If you want "silent and as cool as possible" you need a water loop. The Noctua D14 is very quiet & pretty cool, but the GPU will be loud when fans reved for full load.
Air flow design looks good also. You could put the HDD in the path of the bottom frontal fans so they can get some air across them, as they get a little warm after extended use.
Air flow design looks good also. You could put the HDD in the path of the bottom frontal fans so they can get some air across them, as they get a little warm after extended use.