1) You aren't going to be happy with my answer, but buy everything new (or if you are lucky enough to find one, a used copy that doesn't have any highlighting in it). You cannot, cannot, cannot get by with going to the library and copying cases. Not only would you end up paying to copy 90% of the book, but it would also waste the precious free time you have 1L year. Every night you will have 20-40 pages of reading per class, which works out to about 3-6 cases per night that you need to master for the next day's class. Until you know what you are doing (read: November), you will probably want to color-code highlight the important details of each case for when you get called on. Most people, myself included, will use the system from Law School Confidential, which involves highlighting the holding in pink, the important parts of the dissent in orange, the facts in green, cited precedent/cases in blue, and the legal reasoning in yellow. I found it worked very well for me and helped prevent me from freaking out when cold-called.
2) The book sale is basically only for supplements (every once in awhile you'll get a text, but rarely in good condition). I would go to the bookstore ASAP and buy your books. The undergrads start to come back to campus on Sunday, and when they come back the bookstore becomes an absolute zoo. Beat the rush if you can.
3) You need the latest edition in every class. Occasionally you can find an older edition that will work just as well with the exception of a few new cases, but you don't want to find out that half of the cases have moved around and spend extra time trying to key your book to the syllabus.
4) I swear by the Examples and Explanations series for all my classes. I don't learn very well from the Emmanuel/Gilbert type of supplement, but everyone is different. A universal truth, however, is that Glannon's Examples and Explanations book for Civ Pro is the best survival tool for that class, period. It is a must-buy.