You'll want a lot more ventilation than "a few holes".
Especially here in NC, you don't need to "keep in heat". Our problem is more likely to be overheating.
I have that same plate and I *do* use dual heat with a heat lamp when it's below 50F -- using the lamp to keep the area around the plate above 50F and to keep the water thawed. But once it's over 50F or the chicks are past the new hatchling stage I pull out the lamp. They plate doesn't heat the space, it heats the chicks in contact with it.
Its just as important to have a cool area in the brooder as a warm area and fresh air is critical to birds' delicate respiratory systems.