I have been assembling my homebuilt router for a while and I am at the stage of calibrating the axes.I intended to use LinuxCNC as I have a fair amount of familiarity with some Linux distros and found it quite straightforward to download and install the software.Like Mach 3 is will work with a parallel port,but with Mesa card,you can run it from an ethernet port,which is probably what I will eventually move to when the elderly computer finally goes to the dump.I did experiment with an Arduino in case it was actually easier,but found myself in a confusing world of sketches and github repositories.To somebody familiar with that environment,GRBL may be an easy option and it certainly is an inexpensive one.
My suggestion is that you download the LinuxCNC iso and run it as a live DVD to see what you thing of it and to do the same for GRBL and then see which feels more comfortable.