4 of 6 followed the suggestion to structure as question and answer, not indirect code posting.

I want to use several emacs configurations/versions simultaneously…

…so that no configuration disturbs each other, each with their own configuration directory and elpa repository. I heard about the trick with symlinking ~/.emacs.d and ~/.emacs, but that is not what I want, because it'd be best if I can run my default emacs installation and simultaneously a testing installation (new emacs releases) or another setup like Spacemacs or Prelude.

Is there any decent way to do this?