Do I need any materials for the classes, and where can I buy them?

Yes, you will need a book for your Dutch classes. Here are the specific books needed for each level:

Dutch Experience 1-4 (A0 – A2): “Nederlands in gang”
Dutch Challenge 1-3 (A2 – B1):    “Nederlands in actie”
Dutch Deli 1-3 (B1 – B2):               “Nederlands op niveau”