It's a total pain in the ass, as it has apparently not been tested for x64 systems.
Now I've reached a point where I can't figure out the problem on my own.
The second-last point tells me to install "esptool_0.0.2-1_i386.deb".
But the installation fails saying "package architecture (i386) does not match system (amd64)".
And there doesn't seem to be a x64 package available: https://github.com/esp8266/esp8266-wiki/tree/master/deb
Is espressif not supporting x64 systems? (Why is there a x64 Debian section then?)
Is there a guide to set up the toolchain that has actually been tested?
I'm on Debian 8 (Jessie) x64 btw.