Can I use topics from many different books for content for a course?

Absolutely. While the volumes in our library have been developed to serve as coherent, connected treks through a particular area of mathematics, they are largely made up of chapters/modules that can be considered outside of the context of the book. In fact, several of the DAoM authors do exactly that when we teach. For particular information on the modularity (e.g. prerequisites, logical dependencies, etc.) see the mixing it up blog and the individual teacher manuals for each volume.