All the apps are sandboxed. But They can still talk to each other when they're in the same profile, as long as its mutually agreed.
All the social apps that you speak about are the same from wherever you get them. They're privacy invasive. Its best to use them if you want in a sperate profile. Even if not, its still better using them on GrapheneOS than on stock android.
You could also try using the browser versions. I do that with some stuff when I don't want the apps on my device. I actually use separate browsers for separate groupings of apps.
Aurora store is a mirror of google play. The apps themselves are no more or less privacy invasive. Its more private as you dont need to sign in like with google, possible less secure as your putting a middle man in between you and google.
If I were you, to start, I would just install google play, keep the main profile, and just use it as you would use android previously. See how you go and change it up later if you want. Youre already gaining everything simply using GrapheneOS. The extra mile is there if you need it.