Thought this was an interesting article worth sharing:
Orange Pi is working to steal the throne of Raspberry Pi
A 400W air cooled spindle should do you well. They are not too heavy and can be mounted really easily to the Z-Axis. They usually come with a PWM which lets you control the speed either via a potentiometer or via software.
Take a look at: http://www.makerstore.com.au/400w-spindle-and-pwm-1/