Replacing the Panoramic depends on your other Cox services. For example, do you rent their wireless cable-box for TV service? Do you subscribe to landline telephone service (Cox Voice)?
If so, you'll need to keep the Panoramic connected to the ONT...use the Panoramic as your main router ("Gateway" router)...and connect the Orbi as an Access Point to your network (Panoramic).
If you don't need the Panoramic...
1. Yes
2. It won't. Return it.
3. Yes. No.
Communications arrive at your house as light. The ONT then converts the light to electrical signals (Ethernet). After the ONT converts, the ONT passes the electrical signals to whatever you have connected to the ONT...in this case, the Orbi. The fewer devices between your ONT and each computer, the better.