Great Danes are a giant breed.  And with a giant breed comes special needs.  Please take the time to educate yourself on some of the health issues and special needs that danes have. 

The Great Dane Lady website contains some wonderful information on danes.
The Great Dane Club of America
Danes On Line forum
All About Great Danes.com
The Great Dane, Model of Nobility, by Jill Swedlow (book)

There are many who hold strong opinions about whether or not to crop.  The bottom line is, to crop or not to crop is a personal decision that you must be comfortable with.  Depending upon your experience level, there can be quite a bit of time involved with a newly cropped puppy.  All About Great Danes provides some good information to help get you started on your cropping research.