Robyn, you have picked an excellent time to cross the pond and visit Mickey!
My family loves to load the minivan and drive down to Walt Disney World the day after school is out. Hitting the parks before most families take their summer vacation is ideal if you wish to avoid heavy crowds. Since you are arriving several weeks before most schools in the states finish for the year, you should find shorter queues and more seats on the bus since few parents take their children out of school so close to the last day. Be prepared for an influx of guests during your first weekend since Monday, May 26 is Memorial Day and many Americans have the day off.
Star Wars Weekends are typically held in late May and early June. As a fan of the saga, I believe this is another reason you made such an excellent selection of dates for your holiday. Seeing Darth Vader get down and boogie at the Hyperspace Hoopla, meeting R2D2, and being greeted by Stormtroopers at the gates is galactic fun. If, however, you are not fond of Wookies ( is this even possible?), you might want to hit Disney's Hollywood Studios on a weekday.
Enjoy your time with the mouse.