Brauche ich unbedingt einen (Schwenk-) Lüfter in meiner Growbox?

Yeah, better take a venti.

I have an EC fan that works well even on the lowest setting. And since my box is next to the bed, it's also quiet. Large diameter requires fewer rotations and is not audible when the tent is closed. They do cost a lot more, though. I would also consider how your wood reacts to high humidity. Possibly use spray adhesive to attach reflective foil so that a moisture barrier is created as well.

Uhhh, erstens ist ein bisschen Bewegung der Pflanze wünschenswert, sodass Stamm und Äste stärker werden. Ich habe wie du oben Zu- und Abluft, bei einem 50x50x100cm Zelt. Dies reicht nicht, um die Feuchtigkeit und Hitze gleichmäßig zu verteilen. Ich nutze bei der Größe des Zeltes auch keinen oszillierenden Ventilator, sondern einen simplen Clip Ventilator auf niedriger Stufe, den ich vom Boden des Zeltes nach oben blasen lasse. So bewegen sich die Blätter leicht und die Feuchtigkeit wird von unten Richtung Abluft gepustet. Auch nachts, gerade wenn das Licht aus ist, steigt die Feuchtigkeit bei mir um 10% Wenn du erstmal dicke Buds hast, das Zelt aufmachst und es riecht modrig, wirst du sehen, dass Umluft gut wäre 😬 Wegen der Lautstärke.. da ist meine Abluft lauter! Viel Glück 🤞🏼🤩

In such a small space, your exhaust fan probably moves enough air that it doesn't stagnate in any 1 location too much. Maybe, go for a slightly overpowered exhaust or have fan on intake too.

Moreover, with the size of the box (despite the LED), the temperature will quickly rise to 30+ degrees Celsius, I'm speaking from experience. A fan and fresh air supply (+extraction), preferably with a carbon filter, are super important. Don't skimp on the wrong things.

I had it, it worked well at first, then there was mold in the flowering stage and everything was ruined. Buy yourself a €30 fan, it's worth it.

Heyho, first of all, I would install the old power strip outside the box. For the air circulation, it really depends on the environment/plant mass, but it's definitely not recommended. By the time you reach flowering, without proper air circulation, you have an increased risk of mold and other problems. There are indeed very quiet fans, like PC fans. At the end of the day, you need enough fresh air between the buds; whether the airflow from the exhaust is sufficient can be hard to tell from pictures.