We are approaching the Adeptus Titanicus release which is expected sometime this month. This is the latest information from sources on its release with suggestions on what you may want to purchase.
Please consider these rumors as none of it is official information.
via anonymous sources on Faeit 212
A lot of what FW has shown off is what will be in the game.
Three main force compositions in the game, and only one will use more than one Warlord, making the Grandmaster box pointless unless you want a lot of Warlords and Knights.
Rules Set is basically the Grandmaster box without the terrain, Warlords, and Knights
However, in truth, all of this is known except maybe the second point.
It's going to be a damn great game though. Would seriously advise skipping the Grandmaster box unless someone wants to do a Myrmidon Battleline like FW showed off in their preview. The cost savings in the Grandmaster box really won't help anyone but those individuals or those that want to make sure they can play with a friend at home.
We still don't know the release date or price either. They have this under lock and key something fierce.