Hi,
As Granard says, there is a forum for Disneyland Paris on Trip Advisor where people who know the resort very well will answer any questions and try to help you to get the most from your trip. The more planning you do, the better experience you will have.
If your child is 6 you should be able to book with the kids under 7 stay and play free offer which is on for most of the year. The best time to book is when they release a 40% off offer, which then drops to 30% or currently 20%.
I prefer to phone Disney and get prices for different hotels and arrival dates, as they can vary a lot. Sometimes a higher category hotel may have a better offer than a budget one, making it cheaper.
Also worth asking your local travel agent if they will give you more discount if you book through them - they need business. My local Co-Op Travel give me another 5% off the Disney price.
Also check with Eurostar ( Expedia ) if you want to consider the direct Disney train from London, Ashford or Ebbsfleet. This is very convenient if you live in the South East or can stay overnight in a hotel (eg.travelodge) near the station for travel the following day.
Check the school holiday dates for schools in Europe, especially France and Spain. French schools break up on 2nd July, but Spanish ones break up in June - around 20th I think. Try to avoid school holidays and weekends, and National Holidays unless you are prepared for large crowds.