I don't have much to add, just that I also need colour separation.
Currently I use indesign to visually check the separations AND to send the print job. I do not like at all the way acrobat pro handles sending the print job. It does not seem to properly remember settings and you have to be really careful every time. Indesign is great in that way. I place print ready pdfs in indesign and print from there, so far it is the best workflow for my need.
Even scribus has some ability to preview separations and print them.
Other than that I am very impressed with Affinity publisher.
