Hi Chris,
There is no real easy transition from Mach3 to Mach4. Setting-up is basically starting out from scratch.
Because Mach4 is a new product from the ground up the only thing that is usable from Mach3 is your .xml machine settings, Port and Pin, Velocity, Acceleration, etc., etc.
The really important part of using Mach4 is that you would need to choose a motion controller which supports all the functions you intend to use - some are better at Turn, some at Plasma, some at Laser, etc. and the Chinese controllers should be avoided at all cost.
Tweakie.