Congratulations on the launch of Publisher. It looks great, and I am excited to get to learn it.
I presently use InDesign, and one feature I found very helpful was a plugin script called index-direct.jsx. By using this script, you could have a full list of the index topics in a separate document, and the script would go through the list and form an index for your main document. A thousand entries were completed in a matter of seconds. I am hoping that Affinity or a script writer will be able to provide a similar piece of software. Cheers.