Thanks for the compliment...it was fun to build, and it's been nice to cook on. I'll try to answer best I can...
1 - I can't really give you a comparison before/after as far as fuel, as I've not cooked on anything but this (in relation to its' size...but if you look at the wood box up front, that's about 12-14 hours worth. I'm usually cooking 10-12 hours, and I've never exhausted that much wood. I add a coffee can of charcoal when I'm first lighting it to help establish and ash bed, but that's it. I burned more fuel in the double drum unit I had, so I'd guess it must be related (plus I'm not losing heat with the thinner metal).
2 - I have let low priority stuff (jalepenos, cabbage) "smoke" in the warmer, but I haven't cooked directly in there. By the time I'm opening it up, I've likely foiled anything with a great deal of mass (pork shoulder or brisket), so smoke isn't an issue. Anything that's still taking smoke would be ribs or chicken based on a shorter total cook time and trying to finish close. They have less need of deeper smoke anyway. I do have to bump up feeding the fire a bit when both are fully operational to keep the cc chamber up, but not that much. I also have the opening directly from the fb to the warmer, which can allow a small bit of ash up...again, not an issue since for the most part stuff in there is foiled. Probably not enough to really worry about anyway.
3 - After everything's warmed up, and vented over (there's a bit of touch to this, so I'm sure I could change it), if I run 250 or so on the external thermos, I'll be running 150-175 on the externals on the warmer. I haven't run a direct comparison on internals, as the warmer is less critical.
Hope that helps. If I had to change anything...well, I wouldn't change much, except to perhaps leave a little more length on the cc pipe. It's just slightly tight loading ribs if I'm really trying to load it up.
Can't forget this vital little accessory:
