You can use google play services and google apps on graphene, it sandboxes google from the rest of your device. If you don’t want it, you install alternative app stores but apps depending on google services won’t work
Contacts and message history in what apps? Export them if you can
What’s a password keychain? Most people use a password manager you’d just log into on graphene




Password managers like bitwarden also function across apps and are not limited to browsers