I am also a bit confused by the term "stability." Other than numbering and the Master Documents feature, Word documents have been very stable since Word 2003. Numbering can be made stable but the buttons on the toolbar/ribbon don't help.

A multitude of styles does not make a document less stable; it may make it harder to edit. Multiple numbering lists are sometimes needed because you can have two lists that are really intermingled. Having those lists attached to styles, though, is vital if you want to be able to edit them in the future. How to create numbered headings or outline numbering in Word 2007 and Word 2010
Changing the start of numbering is sometimes done to indicate that certain parts have been deleted; you keep the original numbers from the original document so references to that document elsewhere make sense.

Style-based formatting is far preferable to direct formatting.

Under no circumstances should the Master Documents "Feature" be used routinely or on documents that are going to be further edited.

The problem "char" styles do not develop in Word 2003 and later but may be inherited.

Documents should not be used as the source for new documents. Period. Templates should be developed for proposals. The chance of error rises exponentially basing documents on other documents based on other documents.

New versions of Word allow limitation on styles to be used. See Chapter 50 of Herb Tyson's Microsoft Word 2010 Bible. Note that this also limits ability to add section breaks. This is on the Review Tab (Restrict Editing) or the Developer Tab.

A key thing is numbering. That is most likely to raise problems in documents that go through heavy editing when the numbering is not properly based on Styles.

One option on numbering is to use SEQ fields that are incorporated in AutoText entries. This is essentially bulletproof.

You may want to modify the Ribbon in your templates to completely remove the bullets and numbering buttons (or attach them to SEQ fields and AutoText in some fashion). Removing the buttons is relatively easy. These modifications, though, are done using XML editing, not through the Modify the Ribbon commands in the user interface. Customize the Ribbon (It doesn't take rocket science).

With these modifications, you can also limit access to other Word features from most users.

Probably the biggest cause of document corruption in the last five years is people trying to edit (or save) documents on flash drives and DVD-RW. Word does not work well with mobile media; never has.