Writing Process: How do I approach both reading and writing?

Today I performed a new process in regards to writing the thesis. I organized all the books I believe will be useful in writing the thesis into a spreadsheet (about 120 books in total). Seeing the sheer volume of this I quickly realized that there is no way I could read all these books and meet my deadline of finishing the work by the end of September. Something needed to be done. I quickly created a binary Y/N column that defined whether I absolutely needed the book or not. This eliminated 41 books from my must read list (which is good), but ~80 books remained (still not feasible). So then I created "read" and "summarized" columns with the same binary form of Y/N. This cut the list further down to 65 books. Still not good enough. At this point it became clear that some narrowing of my focus would be needed. With the outline of the thesis in mind, I began creating a priority scheme of ranking each book with a one through five rating, with one being the most relevant to the chapter outline and five being the least relevant. I figured that I would definitely have to read everything with a one priority first, and then worry about everything else later. This cut down the list to 28 books - a very manageable number. But it does highlight that I can't do an in-depth reading of everything. Some books will be to be read in an overview or cursory style while others will need to be more deeply explored. All in all, I know where to focus now and have a plan for moving forward refining the outline and getting ready to write, which I want to start in earnest in August.