(Not a teacher)The 2009 marked the opening of our New Diamond Showroom, thanks for your support and good wishes.
We wish you a wonderful year ahead full of blessing and happiness. May this New Year 2010 will be more prosperous for us all!
The most obvious errors I see are:
"The 2009 marked the opening..." - Remove the first "the".
"May this New Year 2010 will be more prosperous..." - Certainly, remove the "will", as the "May" and "will" don't go together. Also, saying, "this New Year 2010" sounds awkward. Perhaps just, "this New Year", or just, "May 2010 be more prosperous"?
- For Teachers