Quick update: I finally had time today to take a closer look at everything, so I removed the fog lights and grilles...
Result: The lower control arm is actually quite dirty, so I'm going to remove the front bumper tomorrow to completely verschandeln it.
Then I will replace all the seals that are within reach (unfortunately, I only received 3 from the dealer; the price is 10€ for 3 seals and 3 metal clips

).
When the grill guards and fog lights are installed, the airflow to the LLK (low-level cooling) is significantly improved. With the grill guards and fog lights, only about 1/3 of the area is exposed. In the future, I will also remove the fog lights when I change to summer tires, as I unfortunately need them more often in the winter.
Jedoch gibt es keien passenden Grill um ohne Nebler zu fahren, wie zb. Ulf has it.
All the available grills are either fitted with the hole for the mister or have that spot closed off. Unfortunately, this isn't a very aesthetically pleasing solution, and I need to figure out something better... it shouldn't look too makeshift.