For TDL it's good to get a FP for Monsters and go straight to Pooh to ride it before FP kicks in. Then I would get a FP for Splash. Must do's are the parade if it's running, Pooh, Monsters. Tiki room is also unique to that park and has an English assistance device. Canoeing is also nice at this time of year. For restaurants Blue Bayou has a nice atmosphere and Grandma Sarah's has great theming and is more casual.
At TDS because two shows are happening in American Waterfront the FP's run out there first. Start with Toy Story FP ride Tower and get FP for Journey. Everything pretty much is a must do at this park! I really recommend Big Band Beat!, you show go to the first showing so you do not have to worry about the lottery but if you don't want to wait in line give the lottery a try first. I really like the wine cellar room at Magellan's lounge but it's a little pricy and if you choose to do this you should make a priority seating reservation in the morning. For something more casual Ristorante Di Canaletto is good Teddy Roosevelt Lounge is nice to take a cocktail or coffee break and has great theming. If possible you should catch Easter in NY in the evening rather than the day time, Welcome to Spring and Springtime Surprise are also really cute but all in Japanese so you may want to check the English description on the website if your Japanese is not so strong.
Hope this helps a little, I think the crowds should be pretty manageable!