Yes, pay with cash if you can. If you don't put a sim inside, use esim, VPN from day 1 you are good. You can change imei number but take note its's illegal in most countries
However if you do, you can loose pixels's identity. Just swap IMEI with a phone that will never get back to the network in the same country with the same IMEI as it will be flagged as both are using the same number.
Don't install twitter, Instagram and other closed source apps and login via browser if you havey to on other user account inside the grapheneOS with setting that clear session and nothing run the background after you log out from that account and get back to the main one
If you get pixel 6 or 7 you may need to connect with WiFi once before you flash it with graphene so it's good to be on VPN at this time
Flashing takes just a few mins