Homebrew PCBs

Hi everyone, it's me again. I'm starting to work on a homebrew CNC
machine project. My question is about the motors. I know I need a
stepper motor, but what else? Steps, torque, voltage, etc.

I had an idea for the Z axis. Most of the use of this machine will be
drilling holes, so I thought of a spring mechanism. That is, a
solenoid pushes a spring, which in turn pushes the arm holding the
bit, which may be cheaper than a Z motor and also will let the bit do
the drilling on its own, not forced by a motor. Is this a good idea?

hjf