My recommendation is to use custom templates, esp if the output is an XML-based (or XML-like) format.
When you want to get into a custom converter is when you either have to interact heavily with another library (like Asciidoctor PDF) or you need to create compound output (like Asciidoctor EPUB3).
So start with templates and see where it gets you. Then, you can graduate to a converter if need be. That's exactly the strategy I followed with the Bespoke (presentation framework) converter.
I hope that advice helps.
Cheers,