Looks great vk2003!
How it burns can be slightly different each time, i have had it were its burned a line right through the middle and sometimes just one side. I would not worry too much about it. I always hand load the bottom layer before tipping the rest in to reduce the chance of suffocation (this has only ever happened once but it was due to awful lumpwood producing alot of ash and blocking the firebox grate holes).
If i want to increase the temperature quite significantly after a good steady temp, I always give the charcoal basket a shake with some welding gauntlets (a good stir would also help if you dont have a basket).
For example, in your case once I was ready to raise the temp, I would have took the chicken out to check the coal, stirred the coals after noticing the 'hole' in the middle and make sure I can see some of the holes on the firebox bottom (if its a very long cook i would add some more lumpwood if needed) . Then load grills and food back in and then adjust vents. Should take roughly 2 minutes total.
I only do it if im raising the temp by quite a lot, otherwise i dont bother. I only do it to guarantee its going to get hotter but its not required as it rarely struggles to raise temp on its own.
But considering its your first cook, I think you did a very good job!🍻
How did you find setting the vents for the first time? My first time I was paranoid I was going to overshoot massively....and it took me a while to get to cooking temp due to being too conservative haha