After building it I found just one flaw with the design: the PCIE riser of the last card is being blocked by the PSU (check the picture), which restricts the spacing between the cards. They currently sit at 5cm between each other and I wanted to space them even further apart. But then again than might not bring any better temperatures, so its questionable if wider spaces are needed.
If you want to space them more just either make the case wider so the PSU goes more to the right or put the resting planks for the cards higher so that the riser does not touch the PSU.