The first photo in this linked to post is of Chidorigafuchi in late March. It will give you an idea of what to expect. The crowds will still be going strong in the evening (when the blooms are illuminated).
The thread where the post comes from has more first hand reports of what it is like being in Japan for Sakura in late March. The theme of crowds is stressed repeatedly.

https://www.flyertalk.com/forum/26427789-post4.html

ETA - WARNING! I checked on the Disney Sea crowd calculator. My suspicion about the 5th of April being slightly less packed than the 30th March was off.
http://www15.plala.or.jp/gcap/disney/
30th March is predicted to be (in an equal tie with March the 27th) the absolute busiest day of the year with 54,000 people expected. April the 5th is still crowded, but with a prediction of 39,000, considerably less so.