My thought is ditch the 1610 for a 2010 with BK15/BF15 you can spin it 30% faster before it whips (Ballscrews become skipping ropes at a certain speed the thicker it is the quicker you can spin it)

Also if going the single motor, dual ballscrew route cnc4you do a 4nm nema 23 not sure how good it is but worth investigating.

Also the prices of Hiwin's from cnc4you is very good, the rail is clone but the carriages originals I intend to buy mine from there for my upgrade.