I'd think you would need software like 3ds max to create new models, the other features are just to help you get them in game. This is just my guess on it.
However I would like to know more about the modding tools that are going to be released. Like what exactly they do and how they work. Also will you guys be making any tutorials for them, or just let people that want to know how it all works find out and leave it to them to make tutorials for the others who don't want to learn themselves?