Thinking out loud

[JAZZCNC]

Do you use/need a brake or c/balance on the Y carriage

Depends on which way gantry is positioned and in both cases while motors are powered up then No provided motors are sized correctly.

(I'll call the actual Gantry Y axis and the moving carriage across it X axis.)
If the Y axis moves L to R then the motor Detent and resistance from screw is often enough to hold the X axis while motors not powered.

If the Y axis travels Up/Down then yes you'll need either counter balance or like I used to do on my old machine is always park it upto a bump stop when finished cutting and powering down motors. While cutting or when motors are energised then no it's normaly not needed.

My current machine uses a counter balance but this mostly because I inerited the machine and the motors are under powered for the weight of the gantry which is quite heavy when positioned verticly. So I needed to balance the weight to help the motors while cutting. On my last machine that did have correct sized motors this wasn't needed while cutting.
Even thou I don't need to I still tend to park the Gantry against hard stop when being left for long period to remove pressure from the screws and couplings etc.