I'd like to conditionally highlight past-due dates based on a 3 "workday" grace period.

Example:
If the date a project is slated to start is 11/16/17 and we want to provide a 3 day grace period that includes the start date, the cell shall highlight on 11/20/17 which will identify it as past-due.

Additionally, I'd like to keep a count of all of these cells that are becoming past-due in a separate cell, so if there's a formula for that, it would help a ton!!

All help is greatly appreciated!!!