Wooden terrace - Which type of wood to choose, or WPC decking?

The grooves and the water that remains there longer, as well as the increased surface area, were also reasons for my decision to choose a smooth surface with a slope perpendicular to the laying direction. This way, you have quick and even drying, and at the same time, I can lay the boards parallel to the terrace door and still have the slope away from the house. The invisible fastening for sanding off is a good point. I will keep that in mind.

Take a look at Cumaru. A bit more expensive than Douglas fir or larch but also more durable!

Depending on the width of the floorboards, it may still be the case that one or the other piece of wood is slightly warped and despite your considerations, water could stand for longer in certain spots. It is simply a natural product.

We also laid smooth wood parallel to the facade and did not consider that with our dimensions (approx. 3.5x7m) laying it at a right angle would have been much less effort: wood with a length of 3.5 m can be obtained in one piece, but not 7 m, or rather, the wood supplier said that would become unaffordable. So now it is "patched" in length.
With other dimensions we could certainly have optimized the waste a bit more...
And: the construction in the door jamb would be easier otherwise, but we also have a light well in the way.

But: we really like the result in terms of appearance and size. And all efforts to place the edge trimming exactly to the CM in such a way that no board would have to be halved would probably fail anyway due to execution tolerances. In retrospect, I am therefore not sad that I did not know and consider all these points beforehand.

We also laid smooth wood parallel to the facade and did not consider that with our dimensions (approx. 3.5x7m) laying it at a right angle would have been much less effort:

What do you mean "at a right angle"? Do you mean lengthwise to the facade?

We laid the boards parallel to the facade. The joints between the boards therefore run in the same direction as the house wall. However, it would have been easier to lay them rotated by 90 degrees, that is, at a right angle to the facade.

I can also throw in "Walaba" as a suggestion. We have had it for several years and I would do it again. Advantages, origin,... can be found via google