DEVONthink, Scrivener, and Bookends user here. Not a lawyer, and I’m note sure that I have much substantial to add to all the great suggestions provided by others already. But maybe you can still take something at least a little bit useful from the description of my workflow and my choice of apps.
First thing is the note format. I’d recommend to go for Markdown. It took me a while to get used to it but a number of reasons pro Markdown had convinced me.
As you probably know, Scrivener has a rich text editor. Of course you can write in Markdown in it—as you can do in every writing program, you just might need another app to render it—but that’s not even necessary for using Markdown notes taken in, say, DEVONthink. Scrivener has the great Import & Split function which imports Markdown, structured by headings if there are any, and with footnotes. The latter is really important as Apple never implemented footnotes in their RTF format but came up with RTFD instead which does not work with many apps (none outside the Mac universe), not even with the present version of their very own Pages.
While Obsidian has its own Markdown Footnotes “flavour” that does not work with Scrivener, DEVONthink’s do because they both support MultiMarkdown. MMD allows even two kinds of footnotes and Scrivener reflects this by turning on of them into endnotes. So if you use footnotes (and maybe endnotes) a lot you should use a note format that allows to transport them between apps.
Another thing I’d like to mention is the bibliography manager. Mine is Bookends. DEVONthink sits in the middle of my workflow. Everything I write and collect goes into it, some of it moves out, mostly into a Scrivener project. Sometimes I’m collecting material for a project that already does exist (like a monthly magazine), sometimes material collected in DT at first has to reach the critical mass to become a project at all.
What’s important for me is that, again, DEVONthink is in the middle, but not everything I write—actually the minority of it—is done in DEVONthink. And neither in Scrivener, at least not before the material is ripe to become a project. I’m building texts heavily on atomic notes. Very small ideas, lots are just rubbish, but I don’t judge them at the moment they come to my mind.
For jotting these notes I prefer a lightweight and customizable app that works on all my devices. For a while it was 1Writer because it can save its notes by default in an iCloud Drive folder I had indexed by DEVONthink. But I switched to Drafts although I need an extra step of exporting my notes to DT because of Drafts is not saving its notes openly.
It was the great scriptability of Drafts that make me switch and the comfort of many tiny details—widgets for the iPhone homescreen, even a life widget for the text most important at the moment. So good when you’re brain is set to a certain subject and the ideas keep floating in. And it works even on the Apple Watch, dictating and tagging for the later use in DEVONthink on your wrist!
(Sorry, I don’t want to sound like a commercial. I just got my first Apple Watch a few weeks ago and am so glad it worked out and I did not suffer from gadget fever.)
Anyway, back to what I wanted to talk about, the bibliography manager: When DEVONthink sits in the middle, Bookends kind of lurks above (or behind?) all apps. Whenever I quote something I use a Bookends reference, the temporary citation, to be exact. That means, a note taken on my phone, kept in DEVONthink, and finally moved into a Scrivener project, has an identifier that tells me the source of the quote. And in the final document compiled with Scrivener it will be replaced by the citation in the format I like or the editor or the publisher.
Even when I am reading paper books (love them) and quote them Bookends is there: When it’s a shorter quote I dictate it into Drafts on my phone, if it’s a longer one, I scan it into Drafts. And then I use my little Drafts action that holds the Bookends citations of the book(s) I’m reading at the moment, I just insert the page number, tap on the reference, and get a proper Markdown footnote with the reference tagged “excerpt” which triggers a Smart Rule in DEVONthink.
My point I wanted to make so verbosely is: I don’t now of any other program better to sit at the center of a multi-step and multi-app information/text workflow than DEVONthink, and I don’t know of any better writing program than Scrivener. The other apps involved—Bookends seems to be the best bibliography manager on the Mac for me, but it is Mac only which is a huge con for some—whichever they are, should be picked to fit with these two central programs.