Accuracy expectations of a converted mill/drill

Hi,
I'm new to this list, so please forgive me if this has already been covered.

I recently purchased a ( used ) Rong-Fu benchtop mill. It's in good
shape and is within .001 at extreme x and y on the table. ( I'm also
new to machining so this may not be the correct terminology )

I plan on converting this machine to CNC, servos, gecko drives, etc.

A few questions:
1) Do I keep the existing lead screws or replace them when adding ball
nuts to the table ( x and y )?
2) What is a good ( cheap :-) source for these parts?
3) Given the the machine is in good shape, after this conversion, what
kind of accuracy can I expect?

Thanks very much in advance,
-Max