The RS book says that Castle 'entrance' tickets are not for sale online, but I see them at what appears to be an official site.
RS also suggests using the tour outlined in his book, and from my experience his books' descriptions are usually informative as a guide, The only challenge is reading the book while you look around. I do like to go at my own pace. A private or super small tour is always the best, but am not sure if this is where to put that money. It is hard to find small tours, but I can still look.
Just wondering what others know of ticketing, and what they think of guided tours they have taken.