Giant 20' x 3' x 2' router build

[JAZZCNC]

Agree with Jonathan about being better to use twin screws for Y axis and to some degree that Z axis will be weak for cutting plywood but with just a simple change it could be made stronger to the point it would manage be ok.
It would cost more due to extra components and ballscrew placement wouldn't be the ideal but would stiffen things up enough. I've quickly thrown together a model to show you what I mean.
Obviously I don't know the spacing etc in side the Y axis frame or how you plan to attach the bearings and what spacing but looking at your pics I think there'd be enough room.? Spindle is just there for affect and the real thing would need extra support.