In response to three, I wouldn't say they're actually intelligent, they've just been trained to realize that attacking humans equals pain, and pain is bad. Kinda like how we domesticated dogs and stuff. Also, those elephant Grimm were like hundreds of years old. I doubt most Girmm ever get to that level in the first place. 

And I still think the Hunters are the 'Good guys'. Peaceufl coexistence is not possible at this point, given the example of the giant abandoned city they just had the episode in. 

Also, I think Roman rolls in so much Atlas stuff because Atlas is the country with all the tech, so naturally that's what he'd use.