The top and bottom mounting does pull the z axis closer but not by much and you still need to get a ball screw in there any way. Horses for courses i suppose, easy build or extra strengh.

With regard to the diagonal bracing I meant the node as is in the connection point of all the beams. As you have shown them at 45 degrees then they start at a node a go to the midspan of a beam.

If you think of it as a wire frame then where ever the main beams meet there is a junction then this is the node.