BringForthTheHolyWater Hello there!
How you set up user profiles on your device largely depending on your situation, the apps you use, your threat model, as well as your overall needs.
It is important to keep in mind that even if you were only utilize one profile (Owner), all of your apps are still sandboxed and isolated from one another. For most people, user profiles is not something that's even needed or desirable.
User profiles, however, do provide meaningful isolation beyond what the Android sandbox provides. It makes it so apps that could otherwise communicate via mutual consent (that is where both apps explicitly agree to talk to one another) can no longer do so.
It also makes it so you can isolate your data, in case you need to use an app that requires some permission that you wouldn't like to grant it, such as files/storage access or access to your contacts, for example.
You may also elect to install Sandboxed Google Play in one or some of your user profiles, instead of all of them.
What I'm getting at is that user profiles are a very powerful feature that GrapheneOS keeps improving and expanding on, but it may or may not make sense for you to utilize it. How you separate your apps/usage between profiles (if at all) is something that you'll have to evaluate on your end, based on your individual needs.
Edit: Regarding your question about calls and texts - You can make calls and texts from any user profile, as long as you've toggled that option on for that given profile. It's unlikely to matter which profile you make calls from, however I suppose that it would make the most sense to do it from the user profile that has your contacts stored (if not all of them do). It is important to note that user profiles that have calling and texting enabled also have access to your SMS and call history, so if that is a concern for a given profile, you shouldn't grant it that access.