Your input have made me rethink the setup. When I think about it, it has been hard for me to justify my initial setup.
A couple of followup questions:
Regarding the software, TrueNAS: Should I choose Core or Scale?
I am quite new to both underlying platforms (FreeBSD and Linux) so I don´t have any preference any way.
Regarding the Netapp NAJ-0801 / DS4246 and Netapp NAJ-1001 / DC2246 front: I am missing all the trays/caddies. If there are multiple trays/caddies available, what should I aim to use?
And am I restricted to use Netapp specific drives or can I use all SAS/SATA drives?
Regarding the Netapp NAJ-0801 / DS4246 back: Do I need to add more PSU´s? (or would that only add to the redundancy?)
What is the intended use of the two empty slots under the controllers?
For CORE vs SCALE, if you are trying to host VMs and Apps on the same server as your storage, use SCALE. If you are externally hosting them on another server, use CORE.