There are a couple of ways you could denote a calculation vs. a simple dictionary definition. You could use custom fields (or existing fields) in your terms, or you could store your terms with calculations in a separate package from the rest of your terms. If either of these sounds preferable to you, shoot an email to support@serlio.com and we can walk you through the processes a bit.
In regards to a vision document for each package, that should be relatively simple. At its core, a vision document is simply a document that includes some extra details regarding your project. You can create as many of these documents as you'd like, then attach them to each package as a related document. Keep in mind that these documents will all need to be checked out independently (if you're working in a shared project) before any updates or changes are made, then checked back in. Again, if you'd like more information on how to do this, support@serlio.com is here to help.