Okay, lots of stuff in your question. Let me unpack it a bit.
You’re missing a step there. In VCarve (and others like CarvecoMaker) you define the toolpaths and then “calculate” them. That creates the GCode that the OneFinity uses to run & create your project. That’s the “program” the controller needs. The GCode is generated based on the post-processor that’s selected in the design program (VCarve, CarvecoMaker, Fusion, etc).
You need a post-processor for the target machine (the OneFinity) that is matched to the design software. They’re not interchangeable. So if you have VCarve, you need a post-processor for VCarve and OneFinity. Same for Carveco - you need a different post-processor that is for Carveco & OneFinity.
There are machines that can be driven directly by VCarve - my Shopbot Desktop had a version of VCarve that I could send to the machine vs. creating separate toolpath GCode files and then loading them into the Shopbot’s control software. I can go directly from toolpath calculations and effectively pre-load the Shopbot’s software. The OneFinity doesn’t work like that. But it’s also about $7000 cheaper than the Shopbot
DesignSpark is a design software like VCarve but more like Fusion 360. It lets you create real 3D models with constraints so the model is sized exactly down to the 3rd decimal point (or more if you really want precision but the machine can’t cut any more precisely). VCarve is a “2.5D” program that you can get 3D designs out of - by using two-sided designs where you flip the material to carve out the backside. You can get precision out of VCarve, it’s just not as automatic as DesignSpark or Fusion.
Unfortunately, DesignSpark doesn’t have a OneFinity post-processor. You might be able to use a Grbl post-processor like Easel does, but I don’t know for certain it will work. Or you (or someone else in the user group) can modify a post-processor to match the OneFinity (I did that for my CNC plasma).
Or you can save the file as an SVG or DXF and import it into VCarve, define the toolpaths, calculate them and then use those files to drive the OneFinity.
I found it easier to use than Fusion 360 but any 3D design app is more complicated than a 2/2.5D like VCarve. I use them for different things. If I weren’t making fuel tanks and having the software “unfold” the tank so I can cut it out of flat steel, I wouldn’t need anything except VCarve to do what I do on the CNC router.
Technically I think you can sell $1,000 worth of stuff you make using Fusion 360 to design if you have a Hobby license. A couple of years back it was $100,000 allowed for a “small business” license. But they’ve been ratcheting back the rights they allow for the free licenses. They’re also removing access to features that they’ve decided a non-commercial or hobby user “doesn’t need”.
There’s nothing in the software that can track to see if you’re selling more than $1,000 of products, but you agree that you aren’t and that if you do that you’ll buy a commercial license. You have to do that every year. If they found out that you were selling more, they could take you to court for violating the license agreement. The likelihood isn’t huge but it is an ethical issue that you have to come to terms with. I won’t violate their license terms so I moved to DesignSpark for my tanks. Same functionality but no license restriction.
They wrote the software so they get to decide on what terms people can use it. For free, they limit what they want to let you do. They figure if you’re making real money from their software that you can buy their commercial license. The get to do that. You agree to the terms of the license when you sign up.
DesignSpark is open source based and doesn’t charge for the license and the license doesn’t constrain what you can do with what you make from your designs (you just can’t sell the software).
So, long answer to a seemingly simple set of questions