RaspberryPi - Install Gentoo (headless)

After buying a Raspberry Pi for home automation and a building a little home server, I decided to install again Gentoo as my favorite OS. There a lot of Tutorials out there which handles this topic. Also there are some of them that describe the steps to do for a working installation without monitor and keyboard. So, I want to thank all the contributors, blog an howto writers that have inspired me to write this one. Even if I try to comment every step in detail, this is more like a Todo list for myself.