Don't forget you camera to take pics of the castle. But only outside. No photos nor videos inside :-((
Here is a time planner, which makes it easier how much time to spend there:
Ship ride from Prien-Stock to the island and back:
about 20 minutes each ride
Ride with horse carriage:
15 minutes each way
Walk to the castle: 20 minutes one way
Guided tour in the castle: about 30 minutes
Visit of Ludwig-Museum: 30 minutes
Visit of the old castle: 30-45 minutes
Don't forget to watch at the landscape, the gardens and also calculate some time into breaks and waiting time!
Clothing/Shoes/Weather Gear: We visited in mid-September and the weather had already started to turn cold. I was very grateful for my jacket.