Graphene runs on Google hardware... So deapite getting rid of google, you will unfortunately still have to hand them a load of money.
As far as what device to pick... https://grapheneos.org/faq#device-support
I used to use a pixel 7, recently upgraded to a 9. In the EU on vodafone no issues with anything. Also not when travelling outside of europe.
Seems like the worst part is not too bad, all things considered. All you need is half an hour patience with the fizzy drinks ;) Have to say, hate cycling on the cobbles, but love the look of them in the cities! Also, cobbles generally force cars to slow down indeed.