Re: 0.03mm backlash acceptable, yes/no?
If the mill is new then .0012" is fairly good.
Backlash comes from all the components not just the ball nuts. On of the leading caused in a new mill is stick slip and way friction. After the ways break in the table will move easier and you might get under .001"
I have had a few people over the years report large backlash with a system I knew was tight. I ask them to check how hard it is to move the axes by hand and almost every time the ways were set real tight or the gib strip was binding.
I have seen .008" go to .0008"
After the screws and ways break in you might be able to re shim the screws and get under .0005"
Looks like a nice build, lots of screws.
youtube videos of the G0704 under the name arizonavideo99