In my presentation Managed Metadata A to Z I talk a lot about planning and even mention that Microsoft has provided some very helpful excel spreadsheets that can be very useful in your discovery sessions. I have used these as well as taken these and tweaked them for various clients needs, etc. Regardless, they are a great starting point for a process that can be very tedious.
As stated in my session and provided in my slides these documents can be found on the Microsoft site. However, due some occasions I have found them inaccessible I also like to provide them on my blog as well. Enjoy and if you have any questions please let me know.
Managed metadata services planning worksheet: managed_metadata_services_planning_worksheet
Term sets planning worksheet: planning_all_term_sets_worksheet(1)
Detailed term set planning worksheet: term_set_details_worksheet(1)