There's a part of the deal......do you have a flip-up grate?
Those are good (or grate) for adding coals.....that's what that design is for....
A whole chimney is gonna get a pretty high temp, but that may be just right for what you want to do here.....
A guess might be:
Full chimney, off to one side, START with the bottom vents 1/2 open ( or completely open, then shut to 1/2 after 1/2 hour) TOP vent ALL open......
Cap it & wait 20~25 minutes.....then put on the meat......
The idea here is to heat the bell of the kettle, get temp stabilized, be just a little higher than your run temp & not have to fight the temp down......the shutting to 1/2 open means you won't get a runaway burn right off the bat & can adjust either way by a little to dial where you want........
You know all this stuff already from your WSM, it's just shaped differently......
Assuming you don't have a flip grate, do this:
Do it all the time to add bean pans....
....or, use an old spare pair of tongs to tweeze coals in, but that can take awhile......
If dumping from a chimney, just shake VERY easy a few at a time & you won't get a huge cloud of ash & spatter.....
There's another thread going currently about wind & kettles.....
What you see where the bean pan is sitting can be a 350 degree cook, in the wind & heat.....
I've set a couple butts on two kettles in summer, & it was windy later on while I was asleep, cooked hot 'n' fast without my permission.....