WTools ZX45 CNC conversion questions

I own a Wholesale Tools ZX45 RF clone. I am looking into CNC’ing the machine. I am just starting to look into this, so I appreciate the advice. I have a number of questions that I have not been able to easily find the answer to on the forums.

I noticed that my X and Y have 1 inch or ~ 25 mm screws. Looking at the Z-axis and it looks like it is 1 1/8" or 1 1/4", I didn't put a caliper on it yet. I noticed some guys on here are going with 5/8" ballscrews on the X&Y and 3/4" on the Z. Given these things will be spinning a lot faster, does the smaller size pose any problems? Are there any clearance issues with the larger ballnuts? I have not done any calculations yet, just trying to get the heads up on pros and cons.

I also noticed that my X axis is completely floating on one end, no bearing. I assume you guys are putting a floating bearing on that end? Can it be left floating (no bearing) using a ballscrew?

Also, has anyone tried turning their screw ends? I would like to keep the original bearing supports—looks like a pretty simple lathe job on the ends. I have a WT 12x24 belt drive lathe that should handle it. I was reading that you can place the screw in water and heat the exposed end to soften it up for machining preventing damage to the rest of the screw.

Thanks