Good luck Martin.
Most of the confusion probably comes from the original ASCOM drivers. Using them, as you know, you must set a specific driver to a specific camera, for example your imaging camera to ASCOM (1) and guide to ASCOM (2). Then if you change one of the cameras you also need to change it in the ASCOM setup as well, or find another driver.
The ZWO drivers simply does away with that need by allocating the drivers to whichever ZWO cameras are connected so no need to be changing anything. Make sure the right profile & camera are selected & away you go. Note that even if you leave the imaging camera on the ASCOM driver, it will also be detected by the ZWO driver, which is why you need to check the right camera is selected in PHD2.
Hope it goes well, and if you have any problems while down at South Coast Obs let me know, it's only 30 minutes from here.
Cheers,
Mark