Congrats! Definitely you need to think ahead , what spots around castle you like to take more photos . Also Some people like to shoot it when the castle is light up and the sky is dark wheresa we prefer to do it in daylight.
Disney photography provided two photo session time slots (5:30/ 6:30 am) we could choose from. I remember when our Disney photographer picked us up from the hotel at 6 am and drove us to the MK theme park , by the time we arrived at the castle, the sky's still dark, but I told the photographer, let's take photos inside the castle first, this way,the sky was brighter by the time we take exterior castle photos.
You can make a few suggestions but don't expect the photographer to do every single thing you asked, because she/he wants to get out the park before the theme park opens to the public. The entire session took only 1 hour.