Securing a field and linking the field to a sub form

Good Day,

This request for information may be a challenge but here goes; I would like
to secure a field with certain users and link that field to a sub form that
when filled in would returns a score calculation total within the field upon
completion. If the sub form is not accessed or completed by the user
designated then an email reminder would be automatically generated within 5
days and sent to the user requesting completion of the field. The email
would be sent every day until the field is populated. Once the field is
populated it can only be changed by the user who completed the sub form
calculation.

Please let me know your thoughts and how best to proceed. Also, take into
consideration I am a beginning user.

Thank you for any assistance you can provide