I have a custom column in SharePoint with employee number. I want everything placed into a folder (That contains a non null value) to automatically inherit the employee number in the custom column from said folder. This way I would only need to set the property on the employee folder rather than each file.
It's exactly the purpose of the "Document Set", a built-in feature of SharePoint (for both on-premise and online). This article could be useful to learn about it.
For example, you can create a new document set called "Employee" with a column "EmployeeID". Every document stored in the document set will inherit the value of EmployeeID (the value will be stored at the level of the document set).