Hey, I am creating a basic rolling ball game, much like the template, but I want to create a BB-8 type character like this person did . I don’t know where to start, I already have the pawn with the two spheres, could someone help? Thanks!
Depends how much functionality you want, looks like in that version they drive the momentum of the ball by adding angular velocity towards the rotation of the head. You could make the heads movement separate from the ball, I think that’s how it is in the film, sometimes the head is upright but the ball is accelerating. in which case I’d use one input to control the rotation of the head and one to add angular velocity to the ball.
So how would I go about keeping the smaller ball floating above the larger one? How would it inherit the location of the larger ball but not be permanently attached to the surface, and have its own reaction to forces?
I think you can make two bp actors, one with the ball and one with the head. After that you can get the world location of the big ball (inside the head blueprint) and then set the world location of the head with offset. And then you can make it to move the way you want it. 
Why not just place the head above the ball and have only the ball rotate? You should be able to place them in the same level hirarchy wise. That way the head should stay in it’s position inside the blueprint and the ball can rotate freely under it. If you place it in a way that the pivot point of the head is in the center of the ball you could also add a rotation relative to the direction you’re moving in, so that it basically leans over.
Should be easier and cleaner than trying to controll the position of two separate blueprints at the same time.
Does that make sense? 
Export the head so root is at the center of the body but it’s mesh is above the body by the radius of the body. Then when you add rotation to the head it will maintain the appropriate distance from the body.