In general, you can use AutoText to store large or small portions of text and graphics. See Automated Boilerplate Using Microsoft Word
You can even use the AutoTextList field to make a menu of parts to insert.

Look into using the StyleRef field in your headers/footers. When you link the StyleRef field to a header style used in your "parts" the header/footer changes automatically to reflect the page contents. Then your parts can be stored as AutoText. See also Why use Microsoft Word’s built-in heading styles?

If that won't work for you, for parts with headers/footers it gets much more complex. This is because to change headers/footers you need to insert a section. Each section has potentially three different headers/footers and may or may not continue some of them from a previous section. See Sections / Headers and Footers in Microsoft Word 2007-2010

I have not tried storing a section break set the way I want in an AutoText part. If you try it, please write back and let us know whether it works.

Otherwise, you could have these parts as separate documents and use a macro to 1) Insert a next-page section break, 2) discontinue the same as previous setting for headers/footers, and 3) insert that document in your new section complete with headers/footers.