LimeSurvey 7 opens your surveys in the new editor. The classic editor is still available, for example to use label sets or to change a question type the new editor doesn't support yet. You can switch between the two at any time, and everything you build in one editor is there in the other. The choice applies to your user only. On Corporate plans the new editor is not switched on, so surveys open in the classic editor. See Upgrading to LimeSurvey 7: FAQ.
Click your name at the top right and then Editor version.
Under Editor version (1), click Classic or New.
In the picture: 1 Editor version with Classic and New, 2 the close button.
No. Both editors work on the same surveys. Only the screen you edit them in changes.
No. Each administrator chooses their own editor version.