How we will build the robots?
Will they permanently die when killed?
How many can we build?
Will we be able to build robots to guard settlements?
Will they take the place of a companion when traveling, or will they travel with you plus a companion?
So far, I think the only answers to all of those questions are "We don't know."
We know the official description on Bethnet: "The mysterious Mechanist has unleashed a horde of evil robots into the Commonwealth, including the devious Robobrain. Hunt them down and harvest their parts to build and mod your own custom robot companions. Choose from hundreds of mods; mixing limbs, armor, abilities, and weapons like the all-new lightning chain gun. Even customize their paint schemes and choose their voices!"
And we know the names (and artwork) for the achievements, you can find them on Steam's Global Stats page:
Robot Hunter
The Most Toys
Headhunting
Mechanical Menace
Restoring Order
I think that's all the official info we have. Anyone else have something I missed?