First of all, N.O. is not cajun.
A good time to come may be during French Quarter Fest weekend. Free bands all around the quarter and along the riverfront.
For hotels, the Monteleone is a nice couples place or the Maison Dupruy for a cheaper option.
As far as what to do, there are tons of stuff. Just make it a point of getting out of the quarter some. You don't want to be one of those redneck tourist who goes to Bourbon St. and wants to tell everyone they have "experienced" N.O.
Check back on the food and drink board as your trip gets closer and you can get great suggestions for meals, based on what you like.