Hi A.G.
In your file, cell C7's data validation isn't working, as it's trying to reach an outside workbook. I'm guessing that happened when you moved the sheet to a new workbook.
You mention that col G changes based on selection, but I'm not sure how. There are no formulas currently...are you wanting us to write formulas here that will pull information from data tables in M:AF? If so, there's obviously data missing in M:AF. Or, are we supposed to fill in the tables in M:AF? Again, no formulas here, so I'm not sure the the relationship between length and month (or Area) should be.