No worries. I hope you have a lovely time! Also to answer some of your other questions you don't need to pre-book fast pass, still the legacy paper system over here!
ADR are a must for some restaurants - I hear the new ratatouille restaurant is amazing and books up quickly (although yet to visit myself).
Absolutly stay on site! Especially over Christmas, its beautiful. We did Christmas time in the Newport Bay Hotel and it was so pretty!!! Also its much easier to get from the train station (which drops you right outside the parks) to one of the onsite hotels.
Yes its blooming cold here so pack warm! Gloves and hats are a must.
I'm super jealous that you're going to Hong Kong too!

My trip is in the planning stages for 2017 so a long time to plan.
And if you're on a budget you can normally save about £20 - £40 per person for a single from London to Marne la Vallee if you stop in Lille but that's up to you as it does add about 30 mins to the travel time.