We’ve done it twice for our daughter.
1st time we did the Courtyard package. Daughter did love it, but we got the reservation late at Downtown Disney. DD loved it, but she saw one of the dresses that other girls were picking.
2nd time we did the Castle package in the park about 2 hours before our ADR at CRT. Worked out perfectly. We planned some FP+ to Anna and Elso, and then had lunch at CRT. So a lot of the pictures from the rest of the day included her full outfit.
Only suggestions now that she has got both packages. We would take a dress she owned, and have her change before her hair is done, to save $100. Make the reservation in the morning, and prepare for a large amount of glitter.