There is a fair bit of information posted here, but I wonder if we could make a list of the custom elements we need to create in addition to the existing 3rd party elements we might use. Each element would comprise a small task for someone.
I find that I create elements as I go along because when I’m working on it I find that it fits better with a separate web component. But I think you can have groups of web components that just do one specific task (like the division-page/sutta-plex/parallel-view/parallels-input elements) and other web-components, like a drop-down-box, that can be plugged in everywhere and that takes various attributes to change it’s content.
In the Menu, there are various groups stated so these could be developed more or less independently.