My Budget CNC Router

[martin54]

Don't use MDF for that part, maybe something like a block of CLS, which ever way you do it you are going to have to be extremely accurate with your sizes.
Leadscrews well from the little I have learned you need a certain amount of speed regardless of how slow you would like to go. So it is possible you will get some sort of whipping with a 10mm leadscrew, don't forget the minor diameter will be less than that, other thing is that I couldn't see any angular contact bearings with a 10mm inside diameter.

[Jonathan]

I couldn't see any angular contact bearings with a 10mm inside diameter.

1 X 7200 SEALED ANGULAR CONTACT BEARING | eBay

However if the screw is 10mm you need to machine it down to have a smooth cylindrical surface on which to mount the bearing. That means the bearing will need to be smaller, possibly 8mm.
The feedrate you get will be very limited by only having 2mm pitch screws and as Martin has said, if the feedrate is too low the machine can be severely limited. It depends what you want to cut. If it's just most wood and PCBs then you can manage with just about anything, but plastics tend to require quite a high feedrate to ensure the tool cuts and does not rub. You can compensate by using a lower spindle speed and single flute cutter, but there's a limit to how low the spindle can be set before you no longer have enough power to make the cut...