ELI5: GrapheneOS questions

edit: thank you all for your replies! They are all very helpful. I am reading through them and will ask follow-up questions if needed.

I made a post some days ago asking about LineageOS, but my curiosity towards Google Pixels and GrapheneOS has been growing. As somebody who has always used regular Samsungs and iPhones, I hope somebody can clear up some questions I have regarding this OS.

I plan that my next phone is to be either a Motorola (LineageOS/SailfishOS?) or a Pixel (GrapheneOS). My first question about GrapheneOS, or really any non-standard OS, is this:

• how does having an account on the device work? For example, Samsungs require a Samsung account and iPhones require an iCloud account. How does it work on non-standard OSes?

My second question touches on built-in apps that you often get with every phone:

• does GrapheneOS have its own Notes/Drive/Photos/Messages app? If not, how does one go about obtaining these? Related question:
• how do I sync my notes/photos/files/etc to the “cloud” of GrapheneOS?

My third question regards the app store of GrapheneOS. I have heard that the sandboxed Play Store is better than FDroid, for instance; what are your thoughts? Do I go for Aurora Store instead? Is there any major difference at all? Is it possible to use multiple app stores?

• note that I likely won’t be solely relying on FDroid since I need some non-FOSS apps (FB Messenger for contacting family for example).

I know that in the privacy community, it’s very common to fix up a cloud of your own (i.e. NextCloud). I have no experience doing this, but is it something I must do when I install atypical OSes? Then comes the question about pricing, how private and secure it really is, which one to choose… and so on.

I understand many of these questions will sound stupid to those who are experienced, but I have not been part of this community very long. Feel free to link any educational videos or articles that answer my questions. I hope to learn more about this subject and one day installing a more secure system on my phone. Cheers!