I guess the snapshot at December 25 (more precisely: block  1630000) is also the IGNIS snapshot (= the moment when your NXT are counted and you get 0,5 IGNIS for every NXT). Is that true?

That is a little bit unclear in the timeline on Jelurida's page, people were wondering about that in the German BCT forum. Maybe Jelurida should clarify that point a bit more.