I need to create a user-friendly, quick and idiot-proof template for several different people to be able to use. First page would have the below 6 fields (preferably in Header, but whatever works!!) in which people would enter the related information. Is there a way to then have all subsequent pages in the document retain just 3 of those fields (proj, re, date) without them having to reenter the related information a 2nd time?

proj: Project Name
re: Subject
to: Name
from: Name
date: August 15, 2016
comm: 1234.56


Many thanks!!

Yes.
It is called the StyleRef Field.
Create a character style for each field you want to show up in other spots and use the StyleRef fields in the Header.

A good alternative would be Document Property Content Controls as set forth by Greg Maxey in this article: Repeating Data (Populating Multiple Like Fields)

Note, the original information need not be in the first-page header, and should probably be in the body of the document. Accessing a header is one more step that can cause problems for novice users. The StyleRef field would require that they be in the body.

Header/Footer Settings Recap