For the DIY Primo, there are many different pathways to control the machine. You might want to take at the V1 Software Workflow document, and the graphic at the top of this topic.
Your steps 1 through 5 will largely be the same for your Primo. You could purchase VCarve, but, at $700, it is around the cost of your Primo build. Most people look for cheap and free CAM solutions. EstlCam is the most popular, with Fusion 360 coming in a distant second.
I wouldn’t recommend it, but it might be possible to use the Planet CNC hardware and/or software solutions with your Primo. It was difficult to decipher their site and products. I would recommend taking the plunge and learning a new g-code sending solution that has been tested with the control board you select.