For some reason the step 3 was required. Without it the GPG keys import
failed.
I use a nVidia graphics card on my Raptor Blackbird, not the integrated
one. So the whole installation process (after the 4th command) wan on a
blank screen. Switching to other virtual consoles (Ctrl+Alt+F2 or so)
didn't work. But after some time (half of hour, I think) the machine
booted into the X11 desktop and was ready to work.