My answer to the initial question is: Configure the opt-in question as "single opt-in", so no email will be sent.
I want to only use one survey link for all steps.
Well, you probably want to match the answers from wave 1 to those from wave 2. That means that SoSci survey must somehow recognize the person who's filling out the second questionnaire. I recently wrote a chapter about individual URLs, but it's only available in German at the moment: Personalisierte Links und Teilnahmecodes
Yet, even close to your question is this manual that explains different options: Multi-Wave Survey