First attempt…
Sadly I figured out that the nipples used were at least 2 different kinds. 14mm/16mm and for different spoke wrenches. They were bought together as a set with the spokes and I obviously assumed they were the same type/length. I was building in the evening while my kids were distracting me (and using only a screwdriver, not a spoke wrench) so I did not notice before examining the build next day 
Anyway now it’s rebuild with some 14mm black nipples (which also looks a bit nicer…)
It’s a KH Spirit hub and build with 367mm spokes (standard KH36 spokes) but with a 4-cross pattern to compensate for the smaller ERD of the Nextie rim compared to the regular KH36 rim. The length of the spokes for this configuration is perfect.
Tube is a stretched Schwalbe SV19 and used 16mm Velox rim tape. Tire is the Vee Tire T-Monster. It was very difficult to mount on the rim. Broke a few cheap tire levers in the process. Tire seated very nicely/evenly as soon as I started inflating.
Now time to build i complete Uni and test drive, but unfortunately that will have to wait until tomorrow…