The food at Seasonal is excellent though it is contemporary Austrian not German. The space's decor is plain but pleasant. They do private events. Acc. to their website, the "secluded" rear dining room seats 16, and the entire restaurant seats 70.
Seasonal photos: http://www.flickr.com/photos/11863391@N03/sets/72157622915332504/
132 West 58th Street, New York, NY 10019