AFAIK the AT-AT is still in high-poly state and I'm not sure if it will progress in the near future as Eric seems to be busy.
The AT-ST is Sharky's, and I think it has a lowpoly. So that might be better for testing stuff out.
In terms of needed animations I assume it'll work out similar to characters, just a bit more limited.
And the head would be handled like the tank main gun turret.