The spreadsheet has also been updated to include GC Grinding and Repairs, to assist with determining GC costs for those sections. In the future I'll be adding a section for element/attribute increases with GC as well as a way to gauge the amount of quests needed to pay for anything GC related.
Good catch, I checked around the grinding page and saw it listed as a 5% chance for C and B rank weapons and 4% chance for A and S rank weapons. It's been added under the notes section. Also I don't know how the inputs aren't working for you as I can't seem to gleam any errors from my formulae. If you can show me where you're opening the spreadsheet at, and what inputs you're using, I should be able to help you further.