Some people like the convection plate. Personally, I just put in a baffle and added lava rock to the bottom of mine for thermal mass. I found that the lava rock helped act as a kind of "heat capacitor" for times when opening the door was necessary, and helped balance some of the spikes and sags in temperature.
I would check the seals on your unit if your temps are out of control. Check the firebox lid, the points where the flanges that hold the ash drawer mate with the firebox, and the seal between the firebox and cooking chamber. That's where most of the air gets in. Make sure the ash drawer closes tight against the box as well.
As far as loading and lighting the firebox, when I'm using pure charcoal instead of wood splits, I usually line the bottom of my charcoal basket with briquettes to "catch" the lump when it burns down. I then fill the basket with lump charcoal. Finally, I load my
chimney starter with enough briquettes to fully line the bottom of it to an even level (so the briquettes are level and the grille on the bottom is completely covered), or I load it half full of lump charcoal. I actually start it sitting on top of my charcoal pile in the basket, and dump it in when the charcoal in the starter turns ash color. I run with my chimney wide open, unless I run into a problem with the firebox burning WAY too hot. I dont usually put any food past the right-hand edge of the door, since it usualy burns too hot that close to the firebox (unless I'm putting a little extra crisp on something at the end).
A stack extension is important to getting even heat across the cooking chamber. A little dryer mated into the stack on the inside and extended down to grate level helps draw the heat horizontally, rather than vertically.
Hope this helps.