[I just realized I did not translate to German...]
That sounds like a wonderful tank!
A few comments on the Tapajos biotope and the fish selection:
C .. regani is quite common (that's my understanding) and a setting in which they are prominently represented doesn't have to be Tapajos-specific.
H. pulchripinnis are also quite common and are primarily associated with the Tocantins Basin, not necessarily the Tapajos.
I love your choice of lemon tetras (H. pulchripinnis) as the numerous schooling fish that complement the rest of the setup. I love lemon tetra and currently have a smaller school (15 or so) in my tank that is considerably smaller than you plan on. Although Regani pike are much more peaceful than other species in the genus, they still grow tall (14cm or so) and I'm afraid some of the lemon tetra won't get past them unless there are plenty of rocks and wooden hiding spots , but also with these hiding places. That would be my only consideration regarding the stocking.
My only other comment would be to add some plants that may be attached to the tops of branches (thicker ones, not thin ones), although I realize that this would be difficult to do in true Tapajos fashion. But it would provide refuge for the little tetras and improve the overall aspect of the setup.
Sounds good! I look forward to seeing it. Good luck with that and thanks for sharing.