After reinstalling the VBoxLinuxAdditions now the mouse works again, instead the linux boot exhibits some weird behaviour, as when it reaches the login page the login form doesn't appear. If I save the state of the machine and then re-open the virtual machine the login screen finally appears. I installed the dkms support and the kernel headers to fix the issue of kernel headers not found.
Regarding the absence of sr0 in /dev, maybe it has a different name in my OS version.