#1: See the small train in the display window of the World of Sweets in Downtown Disney. There’s a little sign there with a stop number for Marceline, Walt’s hometown.
#4: There’s a number 8 in Aurebesh on the wall upper left from the Murley sculpture.
#6: Answer is found on the stagecoach outside Galaxy’s Edge, next to the Disneyland railroad tracks. The “stage” in the clue refers to the stagecoach, which has a crate of TNT on it. The “Outpost” is Black Spire Outpost.
#15: answer is in Tomorrowland, specifically the trash cans at Galactic Grill. There’s new sculptures there of BD-1 holding a sign telling people to separate out their food scraps from landfill trash.