If you could post some pics of your machine it will give people a better idea of the requirements your machine electronics will need. You say your ballscrews are 25mm Dia but what pitch are they? also a 25 mm dia ballscrew with a length of 1200mm will have alot of rotational mass, so the biggger the pitch the slower they will need to rotate which is a good thing on a ballscrew that size. also 100kg is alot of mass to move, Im building a router/plasma table at the moment with 900mm movement in the X axis and 800mm in the Y, the main structure is aluminium extrusion with 15mm Hywin rails on the Y and 20mm Hywin rails on the X and uses rack and pinnion drive and my Y axis moveing gantry only weighs 12kg (without the spindle). Il be useing a 3Nm (425oz-in) stepper motor on the X and Y, and a 1.85Nm (280oz-in) stepper on the Z, all will be nema23 size. As i said some pics of your machine would help alot in figureing out what motors you need.