Copy Master detail records from a button based upon a selection on the form

As soon as you make the parent table related to itself that will be a looping relationship so the Snapchot field will not solve the loop.

One solution could be to have a connected sync table of just the template parent records. all you would need is a title for the record like Project Nam and the Record ID of the original parent table. That record ID will come across as  [Record ID#2], but so you don't confuse yourself rename that field to be called  [Record ID# of Project Template Record]

Then make a relationship where the project template connected sync table has many project records and you will choose which template do you want to use for the copy Parent Child parent child.  The lookup of [Record ID# of Project Template Record] what you would use in the Java script copy parent child formula field.}