The thing with DXF and SVG files not being the expected size when imported into Luban is a known bug, introduced a few versions ago. Older versions may get the size right, but have other bugs/missing features.
The Snapmaker speaks the Marlin dialect of g-code, so you can use any program that outputs that to generate g-code for it. I also wrote a converter for the grbl dialect—it works at least somewhat on output for Carbide Create, and may help with that from other programs.