Hey and thanks for the purchase!
1. Do not assign the controllers directly as IK targets. Add new child gameobjects to the controllers and use them instead. That way you can adjust the alignment simply by changing the localPosition/rotation of the IK targets.
2. (re)calibrating the height can be done like so:
float sizeF = (ik.solver.spine.headTarget.position.y - ik.references.root.position.y) / (ik.references.head.position.y - ik.references.root.position.y);
ik.references.root.localScale *= sizeF;
3. I used to have a Leap integration, but had to drop it, sorry. They keep updating their API very often and usually in ways that completely break all previous implementations of it. Also my leap device stopped working, looks like its broken. The last working integration I had can be found from here if you'd like to give it a shot.