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If you want to have a 750mm cube as the build volume, you will have a lot of issues with wobble on the gantry unless it has wide supports, which make the overall printer much larger. What were your reasons for choosing a moving gantry rather than a Core-XY, HBot or Ender-5 style?

The Ender-5 style has more belts but it is still a very simple x/y/z style movement and with duplicate belts on the Y with a common drive shaft, would keep things nice and tight for what you are doing. The simple X/Y/Z movement would allow you to swap controllers in the way that you want and frame style could easily be made more rigid if you plan to try to add milling or similar later. It's also an approach that allows for the cheaper "rubber wheels" approach now and swap out to linear rails later if required.