Setting up account and emails for client organization

Hi Squarespace community!  I am in the final stage of transferring the site I designed over to my client and I am looking for some help with email addresses in the account set up and permissions.  I have read countless articles but I am not sure what my best options are for setting up their account.

I designed a school website that will have multiple contacts listed in the account, all of which will have the same email domain.  My first issue is the email address for the site owner.  I understand why SS requires an email address not associated with the domain in the event that there are problems and there is still a way to contact.  How would I have my client set up the account when all emails related to the school end in the school's domain name?  The administrator/owner account cannot be a client's personal email address due to longevity and staffing changes.  Can two email addresses be used in the account (for example, could I use my email and then the school email so that there is an email not associated with the domain but they can still be the owner)?

Is it just the site owner that cannot have an email with domain name?  Administrators and contributors can have an email address associated with the domain name...correct?

When setting up the administrator and billing accounts, can I use a generic first and last name for the account?  For example, there is a general email address ("administrator"@email.com) that they want the account set up with in the event that there are staffing changes in the future...can I put "Administrator" as the name in that account?  Same thing for the billing ("billing"@email.com). 

Any advice is welcome!