Ok, I took a quick look a your CNC, it's a nice work Nr1madman! It seems to be finished soon :)

I can't figure out why is it better to build the rails on the moving plate and the bearings on the stationery side. Maybe someone could explain me.
And is it necessary to have ballscrew with preload torque?

I already bought the G540 for my 1st machine but I really like it, it just works fine.

I'm finishing to update my design and will probably order linear rail Hiwin HG20 (1800,1380,300mm) and ballscrews RM2010(1795,1375,295mm).

Really excited to start to build it!