Sounds like you are on the right track from an electronics standpoint. The voltage of the power supplies is not crucial, but the higher the voltage, the less your torque will fall off due to back emf at higher speeds. I would say the 48V will do well. Geckos are great, and should work well with the Keling motors.
What are you planning from a mechanical standpoint? How are you going to drive your axes, and what are you planning on using for linear slides?
Ahren
www.cncrouterparts.com