What are your tips for DSP self-study?
Tips for DSP self-study huh. Well, ...studying 'signals and systems' is a great idea and having Matlab software means you have the tools to learn an awful lot. I think Dr. Steven Smith's book "The Scientist and Engineer's Guide to Digital Signal Processing", which you can read online for free, is a terrific source of fundamental DSP information. Dr. Smith is a good writer. His book is at: http://www.dspguide.com/pdfbook.htm. Smith is a skilled working DSP engineer. That means he knows which end of the soldering iron is hot.

With regard to a free DSP textbook homework problems, I recently learned that Sophocles J. Orfanidis, the well-known professor with the ECE Department of Rutgers University, has made his signal processing textbook available for downloading on the Internet. The textbook is: "Introduction to Signal Processing" available at: http://eceweb1.rutgers.edu/~orfanidi/intro2sp/. Happily, also available at the above web site are:
(1) Errata for the Orfanidis textbook, (2) Orfanidis' Homework Solutions Manual, and (3) the errata for Orfanidis Solutions Manual.

At the risk of appearing tacky, you might consider my "Understanding Digital Signal Processing" textbook. It's been Amazon.com's top-selling DSP book for some years now. My book's been popular not because I'm any more DSP-skilled than other book authors---I can assure you that is not the case---but rather because I have some skill at explaining signal processing concepts from a working engineer's viewpoint rather than a university professor's strictly-mathematical viewpoint. My book costs money. However, I can assure you, I use the royalties from my book to buy milk and bread for my children.

So Anthony, learning the fundamentals of DSP through reading, performing lots and lots of Matlab modeling, and maintaining your enthusiasm, to quote Susan B. Anthony, "Failure is impossible." Good Luck.