Hide a section based on the click of a box in the beginning of the section

You cannot reliably hide content that way. Although content can be formatted as hidden text, whether that content remains visible or prints (even if not visible) is at the mercy of the user's Word configuration, not anything that you might change in the document itself. You can, however, use field coding for conditionally displaying text & graphics. See, for example:
http://www.msofficeforums.com/word/1...html#post52434
Note though that this won't work for conditionally displaying/hiding formfields.

The attachment to this post shows how to conditionally delete content:
http://www.msofficeforums.com/word/6...html#post16062
You may also wish to be able to restore content that has been erroneously deleted:
http://www.msofficeforums.com/word/1...html#post30792
Obviously, though, if you delete the checkbox along with the related content, restoring the deleted content is going to be rather difficult... See also:
http://www.techsupportforum.com/foru...de-606391.html

I note that your document contains a Table of Contents. You'll find it difficult to update that while the document is using forms protections, which your document will require for the formfields to work. Since you'll need to temporarily unprotect the document to add/delete content, you should update the TOC at that time.

Without wanting to place too fine a point on it, that approach is doing nothing different to what you already had in mind. It is not expanding or collapsing the text. All it is doing is changing the font attibrutes to hidden /not hidden.