The Asrock N100DC-ITX uses a 19v power brick so no separate PSU to power the drives. It comes with a 4 pin cable that splits into 2 SATA power.
The case I chose, Silverstone SG13, comes with a 3.5" HDD bracket but you need to mount the drive belly up so you can screw it in. The second drive I want to put where the PCIe slot is, found a nice 3d model for that. The thing is, the power cable would be too short and the drives would be too far apart to reach both.
So I removed the HDD bracket and cut 2 L-shaped aluminum stripes and I screwed the drive belly down. This way the cable now reaches both drives. I know, I could have cut the cable and made it longer but I prefer to avoid playing with power cables if I can.
Turned out quite good. Wanted to share it with other people. Now I need to find someone to 3d print the PCIe HDD holder and find some rubber stuff to put under the L-shapes to dampen the sound of the drive. This is the 3d model, https://www.printables.com/model/385403-pci-slot-hdd-bracket but V2 with the nice feet.
PS the drives in the images are broken so I just used them as dummy drives.
That's about it.
I like the choice of SIlverstone for the case. I got one of those for my proxmox server. It was compact, but not so compact that I left a lot of skin and blood behind after mounting components. I will say that other manufacturers (like Fractal Design just seem to understand how to design an interior a lot better, though.
I also like the case and since the motherboard has power integrated and the CPU is in theory passively cooled, it will be quite empty since I don't have to stuff a PSU/GPU inside it. Initially, I wanted to get the Fractal Ridge but it was to long for the opening in the cupboard where it was going to sit. The SG13 seemed like the best choice, size wise and the 2 drives fit good.
I am planning on putting a 80mm fan at the back which would bring somewhat limited fresh air and on the front a 120mm fan as exhaust to remove heat from the mobo/hdds.