Software Information Req

If you want to use Mach 3, your best bet is to get something like the 'Ethernet Smoothstepper' board. This lets you use a standard ethernet jack on your computer and interposes a DSP so that things still work even if Windows does something non-realtime with scheduling. But the smoothstepper is still only be issuing control signals. So you will need 4-axis stepper controllers. Something like Gecko or Leadshine controllers are common with this setup, so I understand. So here are your two alternatives:

Mach 3 Path:

(A) Mach 3 ($175)
(B) Ethernet Smoothstepper ($200) (technically optional, but a very good idea, especially if your computer doesn't have an old parallel port)
(C) Leadshine controller ($360) or Gecko controller ($300)

GRBL Path:

(A) Universal G-Code Sender (free) or Grbl Panel (free)
(B) Arduino (you have this) ($20)
(C) GRBL Shield (you have this) ($50)

Mach 3 and Mach 4 do have a lot to recommend them. Many professionals swear by them. But given that you already have everything you need now to make your machine work, you might want to consider giving that a try first. Then if and when you run into the limitations of GRBL (of which there are many), you will know exactly what to look for and be in a good position to buy it.

VCarve (and other Vectric software) works perfectly fine with GRBL. I use Cut2D myself with my setup which is still GRBL based even though I do production work on it. All you need to do is set GRBL as the output type in the post-processor dropdown when generating g-code.

-D