What object files do the game run on so I can start preparing some models to Mod the game when available?

The game is on a newer version of the Creation Engine, so I'd say it's a safe bet it uses some form of the nif format still. I think there was a tool floating around somewhere to unpack their ba2 (new kind of BSA) archives. If we got them open we could see for certain.

.nif format, slightly updated. NifTools developers are working on it.

There's a command line tool to unpack .ba2 archives on http://f4se.silverlock.org and a GUI version on the nexus.