Things to look for when adopting an open textbook into your course are well described in this article by Saylor Academy. The issues remain the same regardless of the source where you find a textbook you wish to use.
Measuring the impact of adopting open textbooks is described in the Guidebook to Research on Open Educational Resources Adoption, by the Open Education Group. (CC-BY)
Modifying an Open Textbook: What You Need to Know, by Open Textbook Network (CC-BY 4.0), "focuses on the technological aspects of editing open textbooks found in the Open Textbook Library or elsewhere, and will help you assess the effort, expertise, and technical tools needed. In addition, this guide includes step-by-step instructions for importing and editing common open textbook file and platform types. Finally, this guide provides a basic overview of accessibility considerations and general guidance on where to find additional help." (From the book's website.)
The Open Education Handbook on Wikibooks has a guide on Editor tools for building and remixing OERs.
Authoring Open Textbooks, by Open Textbook Network (CC-BY 4.0), "is for faculty authors, librarians, project managers and others who are involved in the production of open textbooks in higher education and K-12. It includes a checklist for getting started, publishing program case studies, textbook organization and elements, writing resources and an overview of useful tools." (From the book's website.)
The Open Education Handbook also has a guide on Creating and developing OER.
The Rebus Community has a video series on Making Open Textbooks.
For help adopting material into your course pages or other aspects of using OERs, contact Concordia's department of Classroom Innovation and Online Education.