from stepper to servo

A couple of years ago I bought a stepper motor kit from super tech
and built a plasma cutting table, it has worked well but now Im
cutting large stainless sheets and would like to convert it to a
servo motor system. Im currently using a rack and spur gear, and
would like to keep that. Ive read threw alot of material but am still
unsure of a few things in this new and frightening world..

What size servo motor do I need(currenltly using nema 23 stepper)

Do i need to have a qaud. encoder? how many cpr would work?

If im using real time software do I need a controller or is my
computer acting as the controller leaving only motor amps(g320) to
buy?

And last but not least to clear the haze from the battle field. Im
using auto cad to create all my dxf files for cutting, So what
software would be recomended for use with a servo/encoder? Will they
all work regardless of my encoder type and motor size?

THANK YOU FOR ANY HELP OR IDEAS YOU CARE TO SHARE

Chris ironarbor@...