I just posted a question "Is there a way to save and update a tiddler without closing it?"
and got a good answer from Mat.
Once you close a tiddler, you lose your vim settings. But the solution mentioned in the other thread will allow you to save the tiddler without closing the tiddler. This will allow you to extend your Vim working day, only occasionally having to close out tiddlers. Well, I think it will. I haven't tried it yet (
https://tid.li/tw5/plugins.html#%24%3A%2Fplugins%2Ftelmiger%2FEditButtons)
For marking text, I sometimes put in an html mark like <!-- bookmark a --> and then use the vim search routine to quickly find the text and set my bookmarks again.
Back in the good old days, there was an extension called "It's all text" which allowed you to edit the contents of a tiddler in an actual Vim editor and then, when it closed out, put the text back into the tiddler.