You have asked a very difficult question that has taken the electronics industry a couple decades to resolve. Since this is new ground for you and your company, my advice is to stick with the Steinberg guidelines. As for your specific issues: Actual thermal cycling tests are generally...
The main issue is the hole size, not the shape. For example, if an electronic enclosure is made with a removable cover, the main criteria for emission suppression is the spacing between the screws that hold the cover. The small gap between the cover and the side walls is called a slot antenna...
