I have an order for a castle cake next weekend, a bit daunting but since googling I think it is achievable and im really looking forward to trying it out now.
These pages really helped solving some simple problems I was concerned about:
I think I will make lots of sugar paste flowers (like on top of Park cake) and have flowers under each window along the edge.
I also have some edible glitter to make it very sparkly (especially for the ice cream cones when they are iced)
Pink/Purple and White colours.
To feed 20 children.
Not sure whether to use a square tin or circle yet.