Base area in Tokyo

I am planning to go to Tokyo on 1st wk of May. Will be arriving in Japan via Narita Airport. I would like to visit Hitachi seaside park and fuji shibazakura part. Will Tokyo be a good base to stay to visit these 2 parks?

Yes, those two places are on opposite sides of Tokyo so you�fll need to go through Tokyo.
Probably best place to stay is either around Tokyo or Shinjuku station.
Reserve the trains. Specially the express train to Kawaguchiko sells out.