Hello Heiko,
yes, that looks quite neat. The shower tray you have planned now is an 80 x 80 tub. That is a completely normal size.
Our shower tray in the apartment with 90 x 90 was still considered a luxury size 14 years ago....
Now in the house, there is a shower in the guest bathroom with 80 x 90 - I think that should definitely be enough.
The WC you have planned is quite a chunk with 70 cm depth - with a shorter (normal) WC you can also gain some space.
Find out how your definitive knee wall height and roof pitch look like - the usability of the attic depends on that.
We are also building in the greater Stuttgart area, more precisely in the Böblingen district.
Which construction company (also gerne per PN) have you chosen?
Regards,
Dirk