Thanks. That helps a lot.
I am still not totally sure of the point of the /e/ App Store. I am guessing that anonymizing the download of the App is a key advantage (but, as you point out, there may be further surveillance through the App), and that you include only Apps that will probably work with microG. Also, some of the basic /e/OS Apps are probably not in the Google Play Store at all.
This post by Gael on a connected topic seems to imply that the main point of the /e/ App Store is to download anonymously.
Going on to the Aurora confusion, it seems that there is no disadvantage to an App downloaded through Aurora vs. the /e/ App Store, but the use of Aurora itself requires some work to avoid conflict with the /e/ App Store on items that are in both.