George - I know where you are coming from with the briquettes. You could perhaps use them early on to get the temp up and then switch to lumpwood later to cook on.
Actually, thinking about it, they wouldn't sell briquettes if they were no good for cooking, so perhaps they are OK.
I just tried cooking some naan bread on my "MkII" homemade tandoor oven. I was going to open a new thread but there's so little to say, I may as well write it up here. It was a failure, taking far too long to cook.
Afterwards I cooked some of the same dough under the grille and it was much better. Neither was there any hint of a 'smokey' flavour to the first batch, so where's the advantage of using charcoal? It's so messy, even if it is a bit 'romantic'. I doubt if I've ever had naans or anything else cooked over charcoal in a BIR. I bet they all use gas, and always have. I will have one stab at a MkIII oven designed purely to cook tikka. It doesn't need to be very large because a batch of tikka is so small.
My failed MkII oven was made from a medium-sized propane cylinder with at least 12" of insulation all around in an attempt to build up the heat. Inside the cylinder were numerous storage heater bricks, placed to hold and radiate heat from the first hour of firing, being wood and logs, The temperature must have been sky-high at thar point, given all the flames. Then I added charcoal. I would have predicted this set-up should have become hotter than a tandoor but it seems not, if the naan bread is anything to go by. I never did measure the temperature but it's a bit academic if I can't even cook a naan bread. The bread was loaded vertically on to a granite slab, also pre-warmed in all the flames, and designed to resemble a section of the side of a tandoor.