So I'm going to Japan and to be honest I'm pretty lost on what I should do regarding train tickets. I was advised by my travel agent that a national railpass is the way to go but I don't plan on traveling very far from tokyo so I think that will be a waste of time.

Travel wise I'm staying at the keio plaza and from there I'll be going to disney land, Ueno zoo, Akihabara for toy hunting, and mostly just wondering around the city after that, going to shows, sumo tournaments, some of the gardens and stuff like that. So I expect to be on trains a fair bit.

They don't have 7 day railpass tickets for the Kanto region so I would have to buy two three day rail passes at 8000 yen each and then tickets as I need them on the seventh day. Or would it be cheaper to not worry about buying tickets before I get there and just buy them as I need them over there?