First, I'd contact Gemvision to make sure they're OK with the used
version and see what it'll cost you to upgrade. They might have an
additional fee to register the software in your name, to provide
support etc. I don't know how they handle it, so it's worth a call.
As far as whether, it's the "leader" in CAD, that's up to you to
decide. Buying CAD software is like buying a car, very individual to
your needs. What's good for you is not necessarily good for someone
Besides Matrix, I'd look at Rhino, which is what Matrix is built on.
3Design, which has features Matrix doesn't, and MOI, which is free.
As far as how Matrix interfaces with mills, Matrix, as well as the
others I mentioned, doesn't interface directly with your mill. They
will allow you to export .stl files, but you will then have to buy
CAM software to take those and create toolpaths for the mill.
I would recommend that whatever path you choose for CAD, farm your
milling and RP jobs out till you get proficient with the software.
Then look into a mill and CAM software. It's a lot to learn right
off the bat without having to learn how to be a machinist too.