I have decided to slow down my updates on this project, but I do have a few observations. Adding links to the OPML file was pretty easy in Drummer. I missed adding tags to some links, but will make a sweep of the over the next week. I did some re-arranging of categories, as well as added a lot of categories after the start. In the rendered file, I noticed (as well as a reader) that all the entries are fully expanded. I may experiment with trying to flatten the categories. Also, I have not explored using XSLT style sheets to render the OPML file. Still, my biggest benefit so far is that I am now entering links into the OPML file that I would have pasted in some other file, and they are categorized, which helps in navigation.
My Hugo-based zettelkasten site is lagging in updates. I chose to create a single Markdown file for each entry, and I found that it was a significant amount of typing, even though I was starting with text from the OPML file. My favorite feature of the site is being able to view links by tag. I will continue working to get this caught up with the OPML zettelkasten.
Final note: there are lots of good tools out there, this is what I chose to start with, so far it is working for me!
The organization of the OPML file is easy to follow, thanks!