Layout looks OK to me - I've only made one proper control box so far but I went through the same logic as you and it works OK.

Regarding one of your earlier comments - I decided against XLR connectors between the steppers and the control box and wired them direct to the drivers. Where the cables entered the control box there should be a strain relief gland then the outer braiding was twisted and soldered to an earth wire which went off to the star earth point on the DIN rail. The soldered joint was heat shrinked and looked quite neat. I think it was Dean who showed how he does it and I copied that.

The direct vs plug-in question comes down to whether it is actually of much benefit to be able to plug/unplug the motors from the control box and how often you would want to do that. There is the possibility of signal quality problems at the connector / poor connection over time - I understand that loosing the connection momentarily between driver and stepper whilst the are running can upset or damage the drivers for example. If you hard wire them and really want to disconnect a motor it is only a few minutes to loosen some screw terminals and feed the cable out.