I don't think "happy" and "mood" really go together, idiomatically. "Business" is unnecessary, since the postcard is going to a business person (it is assumed that the "success" relates to their business affairs), so I firmly xrayspex's suggestion.
Please, could you suggests some more congratulations.
I am terrible at writing sincere-sounding greetings! You can do what I always do... use Google to find something that someone with more imagination has written.