If you do end up staying in Kaihin Makuhari, the Airport Limousine bus is a lot faster than any other mode of transportation. The train to Tokyo doesn't go through Kaihin Makuhari. I also second the recommendation on the New Otani there, although I also agree that it is a convention/business area and unless you really want to save money, or are really interested in Disneyland, you ought to stay in Tokyo.

My Tokyo weekend day tourist highlights included the temple at Asakusa, Tokyo Tower, and walking around Shinjuku (especially interested on Saturday at 7 pm to see people getting out of work).