Cherry Blossoms usually bloom in April and they last about one week.. it varies when they bloom depending on the weather so it will be a bit of a gamble..

There are some volunteers in some cities who help tourists.. but Japan is not really geared for tourism (I have never seen a tour bus of foreigners, for example).

Martial arts displays... they usually only do "displays" at festivals and so on.. but you have a pretty good chance of seeing sumo in Tokyo..

Buying a kimono is very kind of you!
You might find a cheap one for $2,000 if you shop around