I spent 11 to 13 April at Disneyland.
The first day was cold and raining. It didn't get above 7 degrees (which is cold for this Aussie) and it rained all day until around 9pm. It was double layers, gloves and beanie / hoodie weather.
The next two days were very warm during the day, jeans and tees, but could get quite cool at night, especially standing in the strong wind to watch the evening shows.
I did not see any Duffy jumpers for sale, but lots of people were wearing them. The mashup shirts we saw included Aladdin, The Little Mermaid and maybe Beauty and the Beast from memory. I'm not certain as they're a little loud for my taste.
As for cherry blossoms, we have found them to be great. We visited a few places around Tokyo before Disneyland and they all looked great, although Ueno Park wasn't worth a visit. Shinjuku park, which has a small entrance fee, was wonderful.