Carport drainage, calculate water quantity

Hi, the rainwater volume is clear, for us it's 209 l/s ha according to Kostra -DWD 2010R

Now I don't want a finished soakaway, but want to dig the hole myself.

And that raises the question.
How big, how deep maximum, how far from the boundary etc. You don't really find much on the internet!

The wastewater company wants a development plan showing how big and how deep we are going to build the infiltration system.

They themselves give no information and refer you to an architect, which I personally find a bit excessive.

As large as necessary. As deep as the permeable layer begins. Not at the boundary but possibly in the middle beneath the carport.

The carport will be placed on an already paved area. At the back towards the neighbor, there are 2 x 7 m that are not paved, and on the side another 2.5 x 12 m.

Well then, keep a distance of 1-2m so that the paved area doesn't collapse while digging.

But how much do I have to excavate now.....?

How deep do you think? Your soil report will tell you that or you will see it during the process.