Personally, if I am grilling, I leave the lower grate wide open. And then I control the temp with the chimney vent. And if you think you have enough lump, go ahead and add 2x more. Ha.

Just keep experimenting. You'll figure it out. But agreed, forums are quite useful. This is another decent one...

http://eggheadforum.com/

If there's any doubt, then there is no doubt... The gut don't never lie.