This is very common for first time use on a
WSM. Once you cook a few times, the gaps will seal up and you will get better control over the pit temp. I would suggest you do 5 lbs of thighs at a high heat - if you can get it up there - to throw as much fat rendering onto the interior as possible.
Another thing to consider is the amount of fuel you are burning at once. When I am doing long cooks, I use the minion method - start only 5 - 8 coals, shut down all the bottom vents except for one vent (down wind if possible) about 1/4" open - place those lit 5 - 8 coals furthest from the cracked open vent so the fuel burns toward the vent. Top vent should be wide open. If I am using a water pan you won't see 200F for about 2 hours. It may peak at 225 and hold for 6 - 8 hours and then slowly drop. You can decrease the drop by opening more bottom vent but the fuel will burn faster (hence more heat).
Once you cook a few times in the
WSM and you want to cook fast, don't put water in the pan - you can use sand or clay instead as an insulator and help keep the temp more consistent, use more lit coals initially and control the max temp using the bottom vents.
One of the most difficult things to do is bring the temp on a
WSM back down once it has elevated. It is nearly impossible. Slowly increase temp to desired - don't ramp up suddenly because you won't be coming back down any time soon, even if you shut down the bottom vents.
Another way to quickly season your pit - may be too late for you now - is to save the trimmings from a few briskets and get the pit - if you can - around 300F and the brisket fat will do the same thing as chicken - you're just using something that you have laying around instead of cooking a bunch of chicken your family doesn't want.