You might find this thread interesting. It describes a flexible way of combining block/outline tiddlers into larger components.
However, I’m still in the early stages of designing an edit UI for the components that uses. It’s not proving particularly easy. The closest analogy would be to Streams, but my use-case is different enough that I can’t use it, nor likely even hack my own choices atop it. I may go back to adding content instead, for a while and mull this over some more; the edit UI is something I don’t really need myself. But eventually this would be taken over by someone with no prior TW experience, and it would have to be simple to use, and fairly self-explanatory. That’s hard work!