Does a superuser has full visibility into spending cards of all users?

If the superuser is the only approver of incoming fund requests, yes. Otherwise, they will not see all fund requests.

Superusers are the only users that are authorized to order physical cards.

Superusers can see and reconcile all transactions across all cards.

Registration status is not visible to superusers. If a cardholder can't be found in the user drop-down list when issuing an physical or virtual card, it means that the cardholder hasn't completed the registration yet.