For what it sounds like you’re doing when you say your stl files are b&w you’d be better off creating vector files for the basic design and then using Fusion 360 to create/extrude the object and for the toolpaths.
For more organic/curved shapes and engraving @Skreelink 's guide is really good.
For what it sounds like you’re doing, which I think is closer to doing logos, you probably want to check out this thread: