OK beginners guide:
You have three types of hotel: off site, associated hotels and Disney Hotels.
Disney Hotels have the advantage of mostly being walking distance to the parks, Early opening of the most popular rides, and a shopping service where you can get any souvenirs sent back to your hotel. they are also more expensive and expect to drop a quality star compared to associated and offsite. You can also shuttle bus to the park
Associated hotels are close, have shuttle buses and generally offer better value for money than Disney Hotels. No extra magic hours, no walking distance, no shopping service. My Explorers and one of the others offer slightly bigger rooms but I think they may be one person short of catering for you group size in one room. My Expolers is lovely (fantastic food) I have heard good things about the others
Both of the above offer to possibility of going back to you hotel room for a break between hours. Depending on the day the park does open later certain days in the October half term.
Off site will be cheaper and better value for money. It will not be easy getting back to your hotel purely from the size of the car parks.
I haven't stayed offsite for me the convenience of being walking distance to the park is important. Personally I would stay less time but onsite or associated, it will be a significantly easier stay. if budget is an issue look at the budget associated over the sante fe.
I can recommend if you are checking out prices for associated and disney looking at My explorers (associated, lovely), Cheyenne (Disney, good reviews) and Sequoia (Disney, on my 6 visit next year and a definite fav). Never found the price varies for Disney and assoc whether you buy direct from Disney or not. Don't forget parking and entry if you are doing comparison. If you are buying separate (which usually is cheaper, you need to add the luggage service separately)
NOW transport.
Without doubt the easiest way for you to travel would be Eurostar. It takes you straight to the centre of the complex, If you are at a disney hotel you can dump your bags at the station and they will get taken back to the hotel while you go straight to the park.
HOWEVER I very much doubt Eurostar will be the cheapest. FOR me I is cheaper to fly budget airline into CDG (Charles de guelle), even including private transfers to the airport and from CDG to Disneyland paris. so don't rule this out. if you stay within the shuttle bus transportation system, you don't need car transport during your stay.
offsite I would be tempted to look into an hotel on the train line to marnee de chessey over car.
If someone is happy to drive Eurotunnel offers pretty good value for money and earlier start on the first day of your stay.
Happy to help any further if I can