As well as the Moff himself writing six episodes, we can also expect episodes from Chris Chibnall (Torchwood), Toby Whithouse (Being Human - who wrote the 10th Doctor story School Reunion), Simon Nye (Men Behaving Badly!), Mark Gatiss (The Unquiet Dead and The Idiot's Lantern) and Richard Curtis (Four Weddings and a Funeral).
If there are 13 episodes in total, I would guess that as well as the Moff's episodes we can expect two two-parters, probably by Chibnall and Whithouse. And news already leaked from the set/the new DW trailer suggests the return of River Song and the Weeping Angels and something about Vampires...
The spring can't come soon enough!