TB6600 stepper drivers and Mk3 controller

I'm wiring up a control box with one Mk3 controller and 4 TB6600 stepper drivers and before I power things up I thought I better make sure I have the wiring right.

My main concern is that I'm using separate power supplies for the drivers and the Mk3 controller, 24v for the drivers and 12v for the control board and I'm not sure if I should connect the grounds together or not, or if I should power the stepper driver (5 volts) from the same 24v power supply, using a step down converter to keep it electrically separated from the Mk3 board (so the only connection between the driver and Mk3 would be the EN, DIR and STEP wires). I'm not sure which way is the correct/best.

The TB6600 drivers have a four pin connector for Enable, Step, Direction and +5V, the way I've done the wires is that I connected those to the corresponding pins in the Mk3 board, so the stepper driver gets the +5v from the Mk3 board and the GND connection from the 24v power supply, which seems suspicious to me; or is that OK?

An additional question, two of the stepper drivers are for the two Y axis stepper motors, I made cable that pairs those two stepper motors to single axis connector, I'm pretty sure that will work right but I thought I'd better check.

Connect 5V signal from controller axis output header to 5V input of driver, and STEP DIR ENABLE signals to their dedicated inputs on stepper driver

To answer my own question, the GND for the motors power supply and the controller were wired together to create a common ground between the 12 and 24 Volt circuits.