The build size is theoretically infinite, but in practice there is a certain amount of drift per unit distance that has to be taken into account. The drift is about 0.1% per unit distance traveled, so that would come out to about 1mm for a 1000mm run.
You would need to set up a jig if you wanted to do this precisely. The most sensible approach would likely be to align the corner of the machine with a corner of your workpiece and use that as the origin for the design. Then you set up your design in CAM with respect to that workspace configuration.
^ that thread has more information on it and thoughts regarding potential alternatives.
Because at the moment, all of the screen processing, actuation, and sensing are happening synchronously in the loop. There is already a bottleneck with runtime UI complexity, so any bigger of a display would make this bottleneck worse. Also, these screens are commonly used in smartwatches, so they’re super cheap and easy to integrate. They have touchscreen versions as well, but again that requires more processing. I’ve thought about moving to a display with an embedded processor which would allow for touchscreen, bigger form factor (if desired), and more complex runtime UI.