@GrapheneOS - Thank you to provide some first-hand information.
GrapheneOS Why are you solely focused on the Google Play apps?
Basically, that was the reason for my question here.
In my basic imagination it works like that: Logging in with my account as john.doe@gargelmail.com with Gplay Store installed, I offer much more surface for tracking my data, because the usage of my mobile can be assigned to my username. Meanwhile, I have read quite a bit in this Forum and in the context of GOS in the internet, and this gives me more and more a different point of view. I remember when tracking cookies were a thing to get users identified across different websites. Although the big tech companies do not give much insight, the replies of the admins over here show me that fingerprinting seems to be a thing in nowadays and apparently the way this is done exceeds my expectations.
OK, I see the Advantage of using Play Story as a well-known, working repository, so I get that point of the GOS developer (with the modified, sandboxed Playstore on top).
So let's imagine I go the opposite way: Only use one Owner profile with sandboxed G Play installed. I install all my apps into that profile, including several proprietary apps, some of them supposed to be "invasive". What would be good practice to keep the invasive-ness low? Only giving minimum permission I assume.
Setting Contact scopes for some Instant Messenger so they cannot get hold of all my contact data?
Is there a reliable way in GOS to put an app to "rest", if it is not in the foreground anymore?
Any good recommendations are welcome.
Besides of that, I can only recommend to every newbie to read here and in the documentation, that really helped me a lot so far.