Jennifer,
Good luck with the 5DII!
Your detailed explaination shows that you have carefully thought about your needs and have bought the best tool for the job. I wish everyone would evaluate their needs as well as use have.
From all reports that I have seen, dust shakers reduce, but does not eliminate the need for manual sensor cleaning.
Avoid shooting Christmas light with the 5DII or you will discover the "black dot" issue that have been reported. Canon has acknowledged the problem and is working on (firmware?) fix.
-Paul