I'm a longtime Serif Page Plus user. I downloaded and looked at this and it's beautiful. But I see no support for footnotes, and I don't see the multi-document pagination into book files yet, so this is far from ready.
I have done multi-chapter books in PagePlus with over 1,000 footnotes and I have never had a crash.
Keep up the great great work, but please bear in mind that the original Serif product's greatest strength was the ability to manage long documents with footnotes. Only Ventura Publisher and Framemaker really had these features, and Serif did it right with Page Plus -- I migrated my press's entire catalog into Serif Page Plus. I hope to see the new Affinity Product excel.