You may be overcomplicating a fairly simple thing. The main thing you want to do is avoid hot spots.
The reason you put the baffle in is tokeep the flames and heat from shooting straight from the firebox to the stack via your meat. It sounds like you've accomplished that.
The reason that you drop the stack to grate level is the same . It will also create kind of a "heat bubble" in the cooking area of the oven chamber and reduce hot spots. It sounds like you've done that as well.
I don't know that the ceramic briquets are necessary. An insukating blanket might be of help in the cold weather, but some good hot burning lump c'coal should keep that thing up to temp with no problem.
The only thing left to do is to see if you have any hot spots. You can do that by placing a thermometer around the grate and checking, or you could just cook something and see.
All smokers have a few hot spots here and there no matter what you do. The important thing is to learn you equipment and then cook accordingly.
If you find that you have any particular specific problems, let us know, we'll solve them .