Are taper lock pulleys a good choice for ball screws?

[JAZZCNC]

This is for a diy router milling machine. I'm still in the initial design phase, so I have not ordered any parts yet.

Well, that's a good thing you haven't ordered anything yet because you need to decide if it's a Router or a Milling machine because when it comes to component choice's they are very different, and getting it wrong will impact either machine negatively.

Right now I'm planning for Nema 34 size motors, but that 4.5Nm figure (or motor type) is not final.
I'll figure this out once the dimensions of the machine are locked in.

Again be careful because bigger isn't always better.! . . For instance, Nema 34's, even smaller Nm ratings are often wrong for a Router unless they have high voltage drives because they cannot reach the RPMs before torque drops away. 99% of the time you'll find the same Nm rating or lower NEMA 23 or 24 will outperform the NEMA 34 given the same voltage. This is mostly down to the inductance of the smaller motor being much lower which allows higher torque/rpm's.

Also, look at Closed-loop motors/drives for both machine types as they are much better than standard stepper systems.

I'll be sure to post my design and ask for critique and comments before ordering any parts.

A wise choice and the right approach.