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I have nothing to add except - welcome aboard.
With poultry, a lot of smoke is not your friend. Go easy on the wood and if you have options for your lump, go with the mildest one.
As long as you cook to temperature (160 in breast, 180 in the thigh) it will be a home run as most people are used to overcooked turkey. So, I usually put the breast toward the front of the grill and the dark meat toward the back where it is hotter. Some people take the turkey out of the fridge and put ziplocks with ice cubes on the breasts in order to get the temperature gradient before you even put it on the grill.
To answer your question about the temp drop when you close down the vent, the answer is: it depends.
If the thermometer is reading 325 because rising heat from the fire is making it read that temp, then closing the vents down and choking down the fire will make the temp drop fairly quickly. If the egg has been stable for a long time and the thermometer is reading 325 because of mostly radiated heat from the hot mass of ceramic and there is only a little fire burning that is slowly adding heat to the system - then closing down the vent will not result in an immediate temperature change.
As the ceramic warms up, you will go through a transition where it is intermediate between the two states described above.