CC-licensing course slides
I copied 1 or 2 figures verbatim (with proper citation) from statistics books. 


You cannot release these figures under a CC license.  Even if we assume that you have the right to use them in this case, for example under fair use, you don't have the right to authorize others to use them in potentially very different ways.

However, you can easily get around this by excluding the figures from the CC license that applies to the rest of the slides.  See, for example, this blog post for further discussion of this issue.


  In some parts, I followed (and cited) the content/organisation of the class textbook quite heavily (not copied though).


This is a trickier issue.  The fundamental question is whether your slides could be considered a derivative work of the class textbook.  If so, then they are themselves a copyright violation if done without permission.  If not, then I think you're OK.

I'm not a lawyer and do not know how to draw a clear line for what constitutes a derivative work.  My understanding is that summarizing or explaining another work is not necessarily a derivative work, but for comparison an "abridgment" or "condensation" is a derivative work (under U.S. law, at least).  Where your slides fall on this continuum presumably depends on exactly what you did.  As a non-expert, I'd guess that you're fine unless you followed the book rather closely, but you should consult with an expert about the details of your situation if it really matters.