Hi Chuckles, welcome to Cruise-Chat. Most definitely book as early as possible. Be sure when you book that you let your travel agent know it is for an anniversary celebration. Most all cruise lines will do a little extra, like balloons on your door and a cake at dinner, plus an anniversary song that will definitely put a smile on your face. All cruise lines have their own personality, some are better than others, but they all offer a fantastic value, good to fantastic food, clean accomodations, and amazing crew/staff.
You could get a suite for all of you, but I think it would be better to get 2 separate cabins. As Sandy stated, there are many different catagories to select from. Inside being the least expensive to suites being the most.
If you do not book through an agent, you can book directly through the cruise lines. You will be able to sometimes receive a discount if the prices are reduced. You, however, will be responsible for checking the prices in the same catagory. Then you will have to call and see if they will reduce your fare. Often, they will give you an on board credit if payment has already been made. The on board credit can be used towards your automatic tips, shipboard purchases, or shipboard fees.
Best wishes for a fantastic cruise and let us know which one you select!