Hello, I want to create Due Dates for Project tasks based on a backwards calculation from a set date.  

My idea is when a deal is closed, it will have an "Event Date" field. I then want to create a Project for that said Event. There are a variety of Tasks that are Due 2 weeks before the Event and other tasks that are due 4 weeks before the event.

My idea is to have Flow create the project, then adding templated Tasks list and calculate the due dates based on the "Event Date" from the Deal.  However, I've gone through a variety of the "Actions"  and can't seem to find the right one to accomplish this.

Any suggestions or alternative approaches are welcome.  Thank you!!