I just answered one question. I'll be using Steppers and not Servo as the Servo controlers are about 3 times the price as the ones for a Stepper system. Even Amazon is hawking kits. And Ebay too.
OK - you get steppers, and you get another whole class of steppers, and you get servos.
Within "steppers", there is an ever evolving set of new techniques in driving them, but very old techniques such as half-stepping, and micro-stepping are now normally available in driver boards.
Straightforward 1.8° stepping is harsh and noisy, and torque limited, but there are better stepper methods. Steppers cost about a third or less than servos with both shaft encoders, and high resolution feedback from final motion surface. Servos are pretty much ultimate in control, but very expensive. Over the last five years or so, stepper techniques have evolved to the point that quieter, smoother, more powerful, yet affordable kit is now available.
Look for feedback!
Do
not get plain steppers. Make sure the steppers use feedback. The cost difference is small, but the performance is all you will need.
The choice for control system.
There may be more, but generally, it would probably be between Mach3 (now Mach4 ??) if you are a locked-in Windows user, and LinuxCNC if you don't mind discovering something like LinuxMint, and discovering that LinuxCNC will happily run on a Raspberry Pi, or any old laptop.
Look at the videos in the links text file.
Within them, the folk who make that content do explain everything about how to choose the right motor, and system, and what they did to convert their mill. Easily the most prevalent is G0704 / Weiss-VM25 et. kit. There is huge value in looking at the video content for machines that may not be the same as yours. The principles are the same, and the side links that YouTube show will let you get into understanding the goods and bads in getting the right kit. Pretty much all the questions you have are answered by those folk somewhat better than I can.
Re: CAD
I use the open source FreeCAD. You can get the free, but not open source Fusion 360. There have been whole discussions in this forum about them. I got into one back in October 2020. Link to -->
HERE
Again, there is huge value in checking out the video content. I just went slow with it, trying it with simple examples.
You can have a little explore with this one..
If you want a fast jump-in to your Weiss, then download FreeCAD, open a new project, and then drag and drop one of the .iges model files onto the workspace, and start looking at it. Be aware that FreeCAD has 10 different mouse select regimes. It will default to CAD, which has middle button do PAN, and Shift+Right-Click to flip it around and roll it about. I think that is the AutoDesk way. FreeCAD can use the styles of ..
Blender, CAD, Gesture, OpenInventor, TouchPad, and others.
Although getting into this CNC conversion is something we are both doing, and we have near-identical mills, you may get ahead of me because I have much other stuff to get through first. Right now, I am just steadily putting together a kit box of all the bits I fancy as I come across them. That said, I am here, as are a whole ton of other HM members, who have done this, and who I am sure would be happy to tell you all about steppers with feedback, and what electronics to get, and how to go about this.