I beg to differ, with respect to the Brake Disk on the milling table.
Any good car mechanic will tell, that brake disks should not be trued up on a lathe, as the brake disks by design must have a tiny runout or wobble, 5 thou, say. On a perfect plane the brake pads would seize up. So using a brake disk like this would NOT put the mill into a true position.
I do use a similar approach though: my plate is a sheet of flaaat 10 mm glas. Works fine for me.
Johannes