4' x 4' x 8" Router Build

[JonnyFive]

Finally some progress! This project has been rolling along slowly in between the many other things that I've had going on, thought it was about time for an update.

This is where I'm at:

x-axis:
2010 x 1480mm ballscrew geared down 2:1 from 4Nm NEMA 23 motor
2 x 20mm x 1450mm HIWIN rails + 4 x HGW20HC2R carriages

y-axis:
2 x 2010 x 1750mm ballscrews geared down 2:1 from 4Nm NEMA 23 motors
2 x 20mm x 1900mm HIWIN rails + 4 x HGW20HC2R carriages

z-axis:
1605 x 412mm ballscrew geared 1:1 from 4Nm NEMA 23 motor
2 x 20mm X 400mm HIWIN rails + 4 x HGH20HCA1R carriages

Frame:
The frame is a mixture of 60 x 60 x 5 and 60 x 120 x 5, possibly overkill with the bracing so might think about simplifying it a bit.
I am planning to use a strip of steel with rivnuts to secure the y rails to the frame rather than tapping the frame - thought this would give a bit more adjustment.

Gantry:
2 x 160mm x 80mm in L configuration
Intermediate mounting plates for squaring the x & y axis

I'm at the point now that I really need to tie down some key components so that I can finish detailing everything and have a few questions for the hive mind:

Motors - Are the CNC4YOU 4Nm NEMA 23s the way to go for all 4 motors? Electronics is definitely not my strong point, I'm going to need a lot of help to get through that part of the project!

Pulleys - are HTD5 the ones to go for? I've modelled up 14T & 28T (copied from Joe's amazing design) and there are a couple of things I'm not so happy about. Firstly the motor shaft is not long enough for the pulley when using one with a boss, it overhangs the end which doesn't seem ideal. The alternative is to use a pulley where the grub screw is on the toothed part and it seems like that will munch through the belt as it rotates - anyone got experience of this pulley type? My second concern is fitting the smaller pulley onto the 20mm ballscrew - the shaft is nominally 12mm which looks too big for the pulley to fit, turning the ballscrew down to 8mm or so seems like it might be too weak? The alternative to this is increasing pulley sizes which will make the motor pulley quite large.

Cable chains - What size do I need (I'll be using a water cooled spindle)? Should I use the same size for all 3 chains or should they get progressively smaller?

I appreciate all the help, cheers!