MDM only supports creating a single user via the initial profile. You can create additional users as part of an MDS workflow. If you create additional users here, they will be ignored. It is possible in the future that multiple users can be created.
If you select the Skip Primary Account Creation option, the Setup Assistant will not show the pane for adding in additional users.
If you select the Make user account created during Setup Assistant as normal user, the MDM Profile User Account will not be an admin. The user account will be a standard user.