But the Problem with that is, that I have over 50 different Templates and maintenance would be a nightmare if I were to explicitly list the Templates. So I would prefer if I could just have a preselected Template every time a new Page is getting created.
What you could do to prevent having to type out every single template in every blueprint to either configure reusable settings (so less places to make changes) or create your blueprints (or blueprint parts) programmatically.