You can compare the date column variable with default Empty Date Field value which is '01/01/0001'.
Similar thread: Check for empty date in SPD Workflow
As a workaround you can also create a hidden date field in SharePoint & compare other date column with this hidden empty field.
For more information check: SharePoint Designer Workflow check if date ...
I'm going to give you only a part-answer and another option. Windows Task Scheduler can be used as your 'date trigger', the WTS task can be configured to kick of a powershell script. The end product is that an email is sent out.
I had a similar scenario here, please read the answer for an outline of this method. It's been ages since I did this though, I'...
For 2010 workflow, you will need to use a tricky way to do this without loop. Using two workflows like this blog. Or you may need to set up a windows task which will initiate a workflow every 14 days, check the status and then send a Email
There is no action in SharePoint 2013 workflow to get the user groups & permissions.
Use SharePoint REST APIs to get the user permissions. You can call REST APIs from workflow using Call HTTP Web Service action.
Get groups of user by using user Id:
Replace <user-id> by Id of user.