Hello and welcome!
AaronWeiss What's the best strategy for profiles / what would you recommend?
That depends on your needs. You could separate work from your personal stuff, use them to isolate particularly malicious apps, the likes of Facebook, or curb usage in general. Apps are always sandboxed no matter what, but some functionality like IPC or knowing what other apps you have installed can only be stopped by putting them into another profile.
AaronWeiss I have GmsCompatConfig for Goggle Play services installed, although I'm not sure why.
That's normal. It's a simple file used to teach the play store and its components how to function in the ordinary sandbox if you do decide to install them. It does nothing on its own.
AaronWeiss I cannot figure out how / if it's possible to have my secondary profile have access to the phone network to make calls.
Tap on your second profile, you find some settings there including the option to turn on phone calls & sms.
AaronWeiss If I have setup a profile with all my favorite settings, can I duplicate it somehow or do I have to start from scratch if I make a new profile?
On the same page you can also install apps that are already installed on your main profile, though that's of course not a full replica. Perhaps look into making a backup under settings > system > backup and restoring it? I've never tried it myself so I'm not sure if that will work out.
AaronWeiss 34 apps out of 34 have a network access on my owner profile and I don't know most of them (42/42 on my secondary). Is a normal / a good practice? Should I restrict some of them?
That's fine. Don't alter the permissions of the standard apps, that will only cause problems for no gain.
AaronWeiss I haven't used the fingerprints so far and I was just wondering: who can access my fingerprints if I save them?
No one. What's stored isn't the fingerprint itself, but rather the respective hash, onto the secure element on your phone.