That's a good question !
Depends a lot on what you're cooking, like your P/ loin goes well at a little higher heat...
This pile I used on the ribs the other day ran @ 300 for about 45 minutes, that's with the unlit stuff just barely starting....
I could kind of see how you had the lit load piled on ( harder to tell in a photo after the grate is on )
& it seemed like you're fixing up for a good size indirect grilling....
That's sort of how I arrived at doing this, only I was trying to do ever longer & lower heat types of cooks, with setups right about like you had
Then trying less coals & less coals, each time to get DOWN to lower tempratures....
Problem was I would shoot too low sometimes & then be playin' catch-up adding coals
But all that was good practice & now I'll sort of know ( at least more closely ) "How Much"
This is a set for ribs, small row on each side, burning opposite directions to even out the heat
Those two little piles produce approx. 250, at the grate & then will hold fairly close to that temp as they burn along the row......turning the grate to keep the meat from direct grilling......
This one for pork shoulder is only about 8~10 coals at the start, as it's going to run 235~240
this gets to be sort of a long answer, but I've found that those 8~10 coals produce 235~240
A few more~250
A few more~260
In I looking back at your initial setup, as a guess only, If you closed the bottom vents to say 2/3 OPEN, top vent all open
And then layed in 15~18 coals, you'd be at 280~300 deg. after a 15~20 minute warmup....
Then it would probably stay reasonbly close to that thru the cook, as you've got a decent size coal pack set to burn.......
In using this modified "Minion Method" it will almost always be less than one thinks, to get the right temp....
One thing I've suggested to folks before is do a test burn or two...
You can put a pan of cold water in to simulate the heat the meat will absorb.....
charcoal & wood is (usually) less expensive than food !!
PS: Other Questions, ask away !!!