You can invite colleagues to your agency. Each person gets their own login; never share one account, because the audit trail is what tells you who did what.
Admins can do everything, including managing users and billing. Staff can be limited to particular areas: calendar, acts, venues, payments, messages, broadcasts. So someone handling bookings doesn't need to see the money. Viewers can look without changing anything.
You can put an account on hold rather than removing it, if someone's away.
The last remaining admin can't delete their own account while the agency still has other members or upcoming gigs. Make someone else an admin first.