Just got mine from HK. I really haven't had much time to do anything with the figure, so pictures are pending, but I have to tell you - it looks awesome in hand.
Anyway to answer some of the questions :
Dimensions of throne are - H = 27cm, W = 22cm, D = 17.5cm (approx)
The "cushion" appears to be molded as part of the throne. It's not a seperate piece.
The Throne easily fits a Detolf with space behind for two guards. At a push , it looks like you could have him standing in front of the throne, with the RG's behind the throne, and it'll all fit in a Detolf, but I haven't tried this with him on the figure stand.
I quickly tried him in a sitting position, and with him slouching, his feet touch the floor. I haven't experimented much more, as I want to take my time this evening with him.
I hope that answers some of your questions. It's a really nice figure - don't fret folks