on my egg i keep the bottom vent open a bit more than a cm wide, top daisy wheel vent open about the same or less. this keeps me around 230 degrees with a full fire ring.
Do you leave it open until your coals are ready so it doesn't get too hot?
no. i light my coals with a chimney starter, pour them into the firebox, put the smoke wood on top of that, replace my plate setter, put a drip pan on the plate setter, put the rack on, and close the lid. i keep both sets of vents wide open to give the coals a chance to fully ignite, this takes about 5 mins or something. when the temp on my dome thermometer reaches 270-275, i quickly close the vents to what i said above, like a cm-to half inch on bottom and less than that on top. the internal temp of the smoker then settles down quickly back to 230-240 and just sets there.
the egg, since it's made of 2 inch ceramic, takes way too long to cool off so it's not good to let it get too hot (beyond smoking temp) when you're bringing it up to smoking temp. there's probably a lot of different ways to do it.