The basics necessary for printing seem to be there. Some manual movements might be nice. An outside way of moving pistons and the gantry. Also a fill procedure if the design of the printer allows for it would make life incredibly easy (for instance, keep adding a layer without lowering the build piston until a button is pushed). These are all features that are nice, not necessary. My knowledge of scad is very limited, so on that side I can’t help you.
Also the render function could be split into smaller subfunctions, but that also happens when you work on it more.
Mechanics is my speciality, if you have any problems on that part, I might be able to help.