Redesigning a site with responsive design? The tech stuff can be challenging, but easy compared to the decision-making, process-defining, and organization-wrangling before you even get there. Karen McGrane has a new book on all this stuff called Going Responsive, and this link post links to Chapter 2 of that, published on A List Part.
In other book news, Christopher Schmitt is working on a book around one of those rollout options: retrofitting. And there is a new Ethan Marcotte book as well: Responsive Design: Patterns & Principles.