I'm not familiar with torch height control, but the one you linked may be designed for use with Mach. EMC can interface with darn near anything, but there might be easier choices for EMC. I would recommend asking on the emc-users mailing list or IRC channel:
LinuxCNC.org - Community
As for the rest of the setup, the G540 definitely works well with EMC, so you're getting warmer at least.