Most of what you’re asking has been answered in several different threads on this forum.
The SM tool library is available on the SM support section of their website.
You haven’t said what material you’re trying to cnc so giving input on any speeds or step-downs is impossible. Most materials you should just have rpm at 12000. Acrylic is one of the few exceptions (but not always).
Lots of people have designed things in Fusion, tinkercad, blender, etc and then exported an stl from there. Luban doesn’t have design capability. It can only do very simple settings and toolpaths. There are a couple other programs to create toolpaths, Fusion is the main one.
It’s possible but not recommended. Some people have created some quick change beds but they’re never going to be as stable or as safe as using the cnc bed as it was designed. For light stuff you can probably get away with it. Not for the stuff I do. Use an electric screwdriver if you want speed (look on amazon for wowstick as an example)
Work origin is determined by how you’ve set it in Fusion and then set according to your work material at start of job on SM.
Couple topics to get started:
-S