So, you want the mountains usable and not like off in the distance...
I would make them one Hill... and then cut in some ravines and cut up some harder rocks areas. Keep it in height perspective. Sometimes you don't need the hills high because of the trees you'll add later.
Gently Slope it up and give it smaller levels- then let the Trees do more work- in my opinion. It will be easier to use the camera when playing and yet keep the Mountain look.
You can have a higher craggy mountain areas show where you don't want or need them to travel or where it will be seen yet out of the way. :)
And think about one side of the mountain slope will be more open for better camera movement when playing and yet have the mountain side.