When I first started using my MPCNC, I had zero experience with CNC tools. Fusion 360 was my tool of choice for modeling for 3D printing, so I wanted it for my CNC jobs as well. For an MPCNC, a Fusion 360 machine definition is not required. In fact, I somehow missed them when I first started using my machine, and to this day don’t have one. It is possible that defining one would result in more accurate machining time estimates, but I doubt it makes any difference in the g-code generated.
You do need a Fusion 360 postprocessor that takes your toolpaths and generates g-code for your Lowrider. The link to the latest one is in this post, and it should work for the Mac.
In terms of staying with the Mac, the piece of the puzzle you are missing is the g-code sender that takes the file produced by the Fusion 360 postprocessor and delivers it to your Lowrider control board. If you are comfortable with running your jobs from a SD card, just save your file to a card, and you are done. If you want to send your jobs via USB or even wireless, you have more work to do. Ryan documents Repetier-Host as a recommended g-code sender (over USB). They have a Mac version, though I have seen some issues on the forum with using the Mac version.
As for your under powered PC laptop, g-code sending is a lightweight task. The laptop could be a shop machine for setting up and running your jobs.