We are currently using Scrum and we are evolving into Kanban. At the same time, we are starting a migration from version 1 of our underlying framework to version 2. There is a target date of January 1 for this migration to be complete. This date is not exactly set in stone, but it's a goal that we'd like to meet in order to add new features before our busy season next Summer. Right now I'm trying to figure out how much development effort that will take.
I'm all for the "decide late and deliver early" approach of agile, but I need to figure out if we'll need more developers and how much work it will take to complete this project.
What are some metrics I can use to figure out how much development work will be required for this project? How does this work with Kanban?