The writers have already been chosen. GRRM will write one episode per season. Everything else will be written by
David Benioff and
D.B. Weiss. It looks like there will be between 10 and 12 episodes per season (I can imagine AGoT and ACoK being 10 episodes each and ASoS being 12, just to fit everything in). The current bet is that they'll film the series in Eastern Europe, most likely Romania, as it's easily accessible and they'll have access to ruined castle locations, semi-desert areas where they can film the Dornish stuff and colder climes are easily reachable for the stuff in North, plus you have the Black Sea for all the coastal stuff. The other alternative is New Zealand, however, which seems to be a good choice for bigger soundstages, local effects houses (Weta, anyone?) and a decent filming infrastructure.
Directors are likely to be drawn from the HBO pool, which they share between shows like
Six Feet Under,
Entourage,
Rome,
Deadwood,
Carnivale,
The Sopranos and others. People like
Julian Farino and
Allen Coulter are likely to be among the directors.
Effects houses: Weta (the
Lord of the Rings movie trilogy) do effects for TV shows and obviously have experience in doing large-scale effects shots and providing physical objects like weapon and armour, and doing so on a limited budget. It hasn't been confirmed but it's been pretty widely theorised that
Rome licensed some Weta technologies in order to do the vast (200,000+ soliders) Battle of Philippi in episode six of Season 2, so there may be an existing relationship that can be used as well.
Costumes and sets will likely be done by HBO's internal departments. Again, it'll probably be the same people who did
Rome, and the sets and costumes in that are exemplery.
The biggest problem I forsee is that, given that
Rome nearly broke HBO's bank (and has been blamed for the cancellation of
Deadwood),
ASoIaF may get a reduced budget
