Hi,
I use artcam which can convert dxf into a cutting file.
I have also used both emc on linux and mach3. Different to set up, but both do the same thing. mach3 will probably be the one to use as every seems to be using it so can get lots of help with it.

With the motor size, it depends on your machine, if your running lead screws or ballscrews, etc. What works for one person may not for another. 300oz/in is a good start though. The steppers on my machine are 1700oz/in :>

If you have the right software it's very easy to convert dxf into a cutting file.

Hope this helps.
Dan