Tooling wise what will engrave wood will do alum, the only thing with alum is you may need cutting fluid.
Mach3 will run g-code generated by CAM systems, it will not create code from pictures.
I would start by following some of the links in the resources menu at the top of the forum. Look at Vcarve, ArtCAM etc.
Your machine will determine what you can do more than mach3 will. If your machine can get to the places you need to engrave then mach will engrave on it.
Graham