You might be able to save yourself an afternoon or so by just buying a pre-assembled unit. It is bare bones, but would be more than adequate for a mini mill. The last time I talked to the seller, he had some 381oz. motors he was willing to substitute.
The 381oz. motors with a G540 can take the mini mill to its limits, so it will be plenty fast.
gecko 4 axis drive 4 taig maxnc sherline cnc lathe mill | eBay