You've really over thought this one now.
My Webber has been sat outside for 4 years and it looks exactly the same as it did when I bought it, my last one which my Dad gave me after he bought a new one sat outside for 10 years until I splashed out on a new one.
The B&Q one will be in pieces next spring I watch many a friend buying cheap BBQ's yearly or bi yearly when they fall apart in a cloud of ash.
Can you wait til Homebase / B&Q do their 20% off weekends?
Charcoal chimney, the Homebase one I got I feel ripped off for £10 as it looks like a bit of ductwork I have on site with some hole drilled in, but I wouldn't pay out for the Webber one.
I have a Webber and a pair of tongs, anything else is not required, I don't have a meat themometer, I use a knife and my bottom lip or for pulled meat just jab a big carving fork in vertically and if it won't pick up the meat it's done, WTF is a smoke thermometer? do you really need one? WTF is a two pit thermometer? you are seriously turning something fun into something boring.
Check out my 40 person BBQ thread, had three BBQs on the go and one set of tongs, that was it.