I have done a lot of pixel repairs and GOS installations . Pixels are glued shut. It is repairable but it is quite sure to say that the screen will break if removed , it's kind of like removing two eggshells glued together. Requires a lot of patience and luck to do it without breaking it. Once in it's not harder than any other phone. That said my own has a a 40 euro case to avoid the issues of repairs, I recommend that. Screens are 100 + euros nowadays. So repairs is rarely worth it. Depends on the price you can get the parts for it.

Batteries can be replaced but takes some work and hot air gun to remove glue.

For GOS yeah that's what you want it's the best. And I do everything from debian distros.

Don't use aurora. Instead install GOS implementation of google play on a separate user profile if needed. The user profiles are a lot better sandboxed than regular user profiles and the gapp implementation better than aurora. And most things work without it also.

GOS gets more support than regular pixels but are recommended to not trust after pixel official updates end. For the new ones it's 7 years. Usually GOS gets a year extra of minor updates. Check the FAQ and device support on https://grapheneos.org/faq

I use mine for nearly everything. And there are either FOSS apps from FDroid (and additional repos) or just use the mobile website for non Foss stuff like banking. There are a few exceptions , like Whatsapp that I need but it have fewer permissions and no access to contacts ( there's a Foss app as helper for that as well) . Your headphones will work fine.