Hi John
Welcome to the forum.
For the guys to offer advice on motor sizing they will need some information on your build, are you using ballscrews, dia and pitch, approx weight of gantry ect.
If you have roughed out your intended machine in sketchup or the like, offer it up for criteque. under no circumstances buy any kit until our experienced members have a chance to comment on your design.
Regards
Mike