So, the question is: Is it worth signing "my own" kernel? Of course I can circunvent this problem simply by disabling secureboot... what do you think, is there a simple way of doing that, or should I spend a weekend doing all of it?

I've found this: http://www.linuxfoundation.org/news-media/blogs/browse/2013/09/booting-self-signed-linux-kernel

Can I sign only the virtualbox kernel module, or should I recompile the entire kernel and sign it?

Thanks in advance!