This project is much bigger than just improving articles about sustainable development in Wikipedia. To truly enable people to get sustainable they need more specific guides to what to do and how to do it. This is where Wikibooks comes in. Here we develop handbooks and resources that are practical and of immediate use (and not suitable for Wikipedia).
Obviously there is room for a loot of different books, both in topics, but also in what level they are in. There can be one book on a topic an a broader (and perhaps more academic) level and other books on a more specific and practical level. Having this overlap can make it easier for a student to move between the different levels.
Work in Wikibooks will happen in several parallel activities. One is to try to decide what resources are needed and prioritize these. Another is to find already freely licensed resources that can be used as a starting ground for new Wikibooks. A third is to translate Wikibooks that have reached a quality level like featured book.