I would go with a Chinese theme for Mah Jong. For food, I'd try to keep it to easy to eat stuff like egg rolls, dumplings, fried wontons, fruit, and fortune and almond cookies. If you have an Asian market nearby, they have lots of really good premade dumplings and egg rolls in the freezer case that you can just steam/fry just before the guests come. Tsing Tao beer and tea. You can get all kinds of Chinese-themed (and for that matter mah jong themed) decorations from craft stores or from a web site or catalog such as Oriental Trading (I know there are others, too).

Have fun!