I'm not convinced you can do the styling so people can see what is and isn't available.
What you CAN do is restrict access to people on staff/board logins who need it.
Either you can use LDAP enrolments (https://docs.moodle.org/LDAP_enrolment ) if you have enough rights (or helpful IT people)
OR use a plugin called Auto Enrol:
https://moodle.org/plugins/enrol_autoenrol (basically, you set attributes in your user profiles then police access to pages based on these attributes - you can have multiple rules per page)
We've used the autoenrol plugin successfully before as we don't have access to change things in our AD/LDAP.
Anything to do with moodle Cohorts, someone else who has experience will have to chime in.