Narita airport is about 1hour (bus ride - they called it airport limousine bus) to town. I'm not sure where is Sherton. But, I was staying near the Shingawa train station and took the train to Tokyo Disneyland, Tokyo Disney Sea.
They are 2 differerent theme park - land is kiddies. while the sea would be more appreciate for older kids. Yes, you should use your entrance ticket to get the fast pass and return later for the rides by joining the shorter q. Of course, they limit you to the nos of fast pass you can get.
They have lots of staff on duty and you can ask around. staff are very helpful.
Hope the tips helps.