Tokyo Disney Timing?

My partner and I are planning our month-long trip for next year. We have flights booked to arrive in Tokyo on the 30th of March and leave the 28th of April.

During our trip we would like to spend two days at disney (one day at each park) however I’m trying to figure out when is the best time to go?

I read that it’s the school holidays the first and second week of April. But the 40th anniversary celebrations starts on the 15th of April. So when do you think it will be the quietest days? (We will definitely be going on weekdays too)

Also it is worth staying at one of the disney park hotels or should we stay just around the area?

Any advice is appreciated!