Hi and welcome to GMAT Club!
I hope someone with a recent GMAT Online experience can give you a bit more logistical information. Here is what I know:
1. You do not need to show your whiteboard on the camera. Nobody does basically but you need to show it before/after
2. They will ask you to move the camera around. Is your camera movable or is it one of those iMac things? Either way, you will have to move the camera around to show your room (most likely)
3. You will need your phone for check in and communication with the proctor ONLY IN CASE there is an outage but it needs to be away otherwise
4. Your room needs to be enclosed/contained
5. You do not need a mirror - that's pretty innovative but usually they ask to move the camera around
6. Keep in mind that sluggishness and slight delay of 1-2 seconds sometimes happens when clicking Next button so just something to grind through. It is frustrating but usually people get through it just fine.
7. In case your test is interrupted and you lose time, do not continue the test. Continuing the test assumes that you are OK with the interruption and you will not receive a refund, so if you have a technical issue, you should ask your proctor to file a report about the technical problem and reschedule your test. This is important as if you complete the test and receive the score, you will lose the right to retake for free (this is NOT an official rule but something learned by many the hard way)