I picked up a free (I love having yuppy neighborhoods around me) Weber 22" kettle a month or so ago. It had not been in a loving home so it was in sad shape. However, the lid was perfectly fine so I bought a $4 smoker thermometer at Meijer and drilled a hole in the lid for it - it worked like a charm. I used this freebie lid on my personal 22" kettle as I wasn't going to drill a hole in my own lid.
Cook time? I would budget a solid 8-10 hours.
Temp? I honestly ran this one higher/faster than I like but I was in a time crunch. This flat saw 250* for 6 hours of indirect heat & smoke and then some time in foil. I would have liked 215-225 for 8 hours. You will see/read so much personal opinion on cooking temp and internal temp. I personally shoot for an internal temp of 150-160 and then I double wrap it in foil to finish it out. I don't check internal temp after it goes in the foil, I just shoot for 1.5-2 more hours of cooking.
Full disclosure: I put a 1/4 cup of beef broth in the foil to add back some moisture and to steam it, this works amazing. I had over 1/2 cup of liquid in my foil that I carefully saved to baste the cut meat with. I like to let the flat rest for 30-45 minutes after taking it off the heat before I cut it.
Meat source? Mom/pop grocery store. This was a choice cut they had on sale for something like $2.79 per pound - I grabbed several to have. They are all in the 4.5-5 pound range.
Pre-cook photo. Beef, salt & pepper (50/50 ratio). I put the salt & pepper on the night before and let it sit covered in the refrigerator.
