Cam / EMC

I'm new to the group / CNC / retrofitting. It seams this group
holds a huge knowledge base on the subject. I have a good back
ground in electronics with a primary interest in microcontrollers /
digital logic. I also have a small mill and 2 lathes. I would like
to automate one of my lathes. My main goal is to be able to cut any
pitch thread without the need for all the change gears. I have
installed ballscrews on both of the lathes axes. My first question
is: Will I be able to use the existing 3ph 5hp motor to power the
headstock? I plan to mount a rotary encoder to monitor its
rotation. I also intend to use EMC to control the motion.

What is a good cheap CAM program that produces G-Code for EMC?

Thanks
Mike