You can go through initial setup without having an Apple ID at all but to use iMessage, FaceTime and App Store you will need an Apple ID.
You can just sign up for an Apple ID using your Gmail address and you can add several email addresses to the mail app if you want. Up to you how you want to do it.
You can just sign up for an Apple ID using your Gmail address and you can add several email addresses to the mail app if you want. Up to you how you want to do it.