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

1. Follow the instructions as they're presented and you'll be fine

2. Installing it will make rooting easier, but afik root is not required (though you will be accessing the device at the recovery/bootloader level, something with far more control than root)

3. Yes, pay attention, follow the instructions and you'll be fine though

4. Respect your privacy, allow you to sandbox apps which want to spy

5. Everything should work because of the sandbox function, the same cannot be said for most other custom ROMs unless the Google apps have been installed.

There are definitely some things that do not work with GrapheneOS, though most haven't affected me as I don't use them (like banking apps).

1. A lot of banking apps don't work, especially from some European banks. I believe there is a fairly well updated list available online.
2. Android Auto can be made to work, but it's quirky and you have to fiddle with quite a few settings and possibly give up a fair amount of privacy to get some things going (like navigation). I'm still fighting with this.
3. Many apps will initially not work until you figure out what permissions they actually need and which they can bend on.

I still personally think it is worth it, but I can only speak for myself.