After almost a year of using GrapheneOS I have made an informed decision to switch to sandboxed Google Play Services use. My experience with it was surprisingly positive.
I only use Play Store for a handful of apps that I require, like my banking app, couple of apps that rely on notification delivery and a couple of games that I can play with my son who doesn't live with me. All those apps have only such permissions enabled that they manage to work.
For ease of use I only use one profile. To note, aside from Play Services I don't use any other Google products or services or any social media aside from WhatsApp (and would switch to Session if people who I hold dear weren't ignorant of their privacy). Half of the FOSS apps mentioned in the first post are on my phone too. I changed launcher to Square home for ever present sadness from losing chance to use Windows phones (bless those times of privacy naivity).
I use OpenDocument reader for dealing with documents and Notally atm for notes. I am not happy with performance of Tutanota, app doesn't start on boot and tends to die in the background despite all battery optimizations. I changed all my email communication to it from Proton and now I wish to go back. See what the time brings.
Wherever I can, I revoke network permission and go local. I don't use any cloud services and whatever needs backing up, it's on my USB stick.
My battery life dramatically improved by using sandboxed Google, especially when the device is idle. I probably omitted mentioning some things but to sum this up: I do not mind that Google knows a thing or two about me but I thoroughly enjoy the fact that it doesn't get to peek at what I do all the time and can't access a lot of IDs, as it would on a regular stock Android.
I keep all my apps on one page in app drawer for a clear overview, supported by widgets on the home screen. There is beauty in simplicity. To me using GrapheneOS on my P6a is currently a perfect compromise for a world full of security vulnerabilities and mass surveillance by design and I hope to enjoy it for years to come. It is the only device I use, desktops don't cut it for me, they are one league below and I just don't wish to go that way, only way is up.
My big thank you again to the developers and that one person behind it all and I consider donating within my means again soon.