The movement of the axis is free - I attached the ballscrew nut to the Z-axis earlier today (just uploading the pictures, and then I'll write it up). There is a small amount of play, but I've not put in all the bolts, and of the ones that are in, not all are tight (I think only 8 are tight, and there's 22 in total).

I know what you mean about the brace; I'll have to see what happens when everything's tight (I do need to put another plate in anyway to push the router vertical; this could be made a triangulation piece).

Note that I'm considering that axis the Y axis (based on the previous version and the orientation of the computer models I've made).