We use the following books: Interchange Intro (5th Edition), Interchange 1 (5th Edition), Interchange 2 (5th Edition), Interchange 3 (5th Edition), Basic Tactics for Listening (3rd Edition), Developing Tactics for Listening (3rd Edition), Expanding Tactics for Listening (3rd Edition), and 504 Absolutely Essential Words (6th Edition).
You can buy them according to the teacher’s specification—there’s no need to purchase them all at once, as the teacher will let you know when to buy each.