Have you tried searching for similar posts? There have been many similar questions asked

The tourism board has a good website washington.org, there are also hundreds of threads about things to do on this sub. If you have a more specific question than plan my trip for me you may get better responses.

If you want tours of the White House, you need to set them up now.

There are a ton of options here for history and cool places to eat, so you'll need to be more specific.

The memorials at night. There is something magical about it. Especially the Jefferson memorial.

The cherry blossoms will likely be over by then, but there are other fun "outdoor" things to do. Most tourists stick to The Mall area, where most of the museums are, as well as Capitol, White House, etc. Going to the Lincoln Memorial at night is fun. I encourage you to branch out to other areas though. Some people enjoy a walk along "embassy row", where many of the larger embassies are. It starts at Dupont Circle. There are lots of cool places to eat. Probably helps to search by cuisine in certain neighborhoods, like H St NE, U Street NW, 8th St SE (by Marine Barracks). Another fun activity if you rent bikes or scooters, is to head from the west side of The Mall (by Lincoln Memorial) out to Haines Point. It's a nice little bike ride along the Potomac River. Maybe consider a boat ride over to Old Town Alexandria ? On Sunday afternoons there is always a pretty cool drumming/music/dance circle at the top of Meridian Hill Park (aka Malcolm X Park) at 16th/W St NW (straight up 16th Street from White House). Good vibes and a multi-cultural affair. Nice view of city too.

The orchid exhibit at the US botanic garden runs through April and is absolutely gorgeous if you’re into nature/plants https://www.usbg.gov/visit/exhibits/discover-world-orchids-0