I would do this by saving each 'document' as a building block in the template. You could do the entire thing without coding if you then made use of the building block type content controls.
You could probably do something slicker with a userform to get the user selections but that might be considered overkill if your users don't mind a little scrolling.
The best source of information on how this might work would be Greg Maxey's website. Try this link to explore this option
http://gregmaxey.com/word_tip_pages/..._autotext.html