If you use the web installer provided on GrapheneOS website, you can’t fuck it up. Just make sure you use a chromium browser when you do it, for some reason it crashes on Firefox (but it didn’t brick my phone, so don’t worry)

No root needed, just follow the instructions on the website (read before doing it). You probably could brick it like anything else, but I didn’t and I barely knew what I was doing (and like I said, it crashed on me when trying it via FF).

Neat things they do that Google doesn’t (afaik):

• Auto turning Wifi and Bluetooth off if it’s not connected (security and saves battery)
• Being able to deny wifi permission to an app just through regular settings (Stock androids need root to do that). Like, I use Gboard, but it had no wifi, so it can’t send telemetry to Google.

Notable things that don’t work:

• Some banking apps, really depends on luck. My debit card bank doesn’t work, but my credit card bank does. Check this list to see if your banking app is tested. The reason is out of GOS hands, Google changed from SafetyNet to Play API or smth. If you can, just do web banking.
• RCS is finicky enough on stock devices, but GOS ramps it up to a new level. There’s workarounds, but don’t be surprised if it breaks a few months later. Highly recommend getting your friends/family to communicate with you through a different E2EE app, like Signal, XMPP/Jabber, etc. or else you’ll be stuck with insecure SMS
• Some people have Android Auto issues? Idk, I’ve never used it