Hi, Psid
Your item 1, When you load a file in LazyCam you can post your Gcode, leave LC open, minimize it, Run your Gcode in Mach3, if you need to change it minimize Mach3, maximize LC make change's repost with a different name.
You always have your original DXF files.
LasyCam dose not load Gcode files.
Hope this helps, Chip