Ball screw conversion for Grizzly Mini Mill

Anyone done Ball screw conversions on A Grizzly/HF Mini Mill? What
sizes should one consider when doing. I'm new in this arena and
looking for good advice. I intend to convet my Mill into CNC and
first want to replace the poorly designed lead screws with Ball
screws. I just don't know what dia. or threading to consider. I know
I would prefer it to be in inches rather than metric, but will take
the latter if needed. I plan on doing all three axis, plus add a 4th
for a rotory table. It's going to be a fun and exciting project. But
for now I need to get all the information I can before embarking on
any modifications.

Again thanks for your help.

Shawn