Visit to Disneyland Paris in 3rd week of May on a Friday

Shall be grateful if you can guide on following

a. Till what time trains are available from Disneyland Paris for going to Paris (actual destination will be Aulnay Sous Bois)...will it be available at 2300 hrs.

b. Are taxis also available - which ones are economical and reliable

c. Can we carry a small back pack with eatables etc - with each person - do they allow it?

d. Can I purchase online ticket just a day in advance or does it require longer planning. Is across the ticket counter costlier than online tickets?

Shall be grateful for feedback