I’m not a person who had previously done much messing around with their phone but I have installed Linux on several computers. I put graphene on my phone nearly a year ago and I recall the process being fairly straightforward. I think I just followed the instructions on their website.
Maybe it’s not an “any idiot could do it” level of user friendliness but the examples you’ve listed as stumbling blocks aren’t exactly brain-busters.
I found the instructions on the website to be completely adequate.
https://grapheneos.org/install/web
You’ll still be able to use Google Play and the apps found there, if you want to. I’d heard of people having trouble with banking apps. I access my bank using their website, not an app.
Just understand going into this that the priority is privacy, not compatibility. Maybe keep your old phone around in case there’s some must-have app that doesn’t work but you need occasionally.