A few thoughts for you, ChrisD:
RE: Lump - I have about 2 seasons of using the WSM under my belt (not an expert - but I have had the chance to learn from mistakes). I have used Lump exclusively, and have not had any major problems.
RE: Cowboy Lump - I was dissapointed with it when I tried it. Try a different brand of lump. (USA-made Royal Oak is decent stuff, that is relatively easy to find.) Also, check other links on this site & check the NakedWhiz's website - they rate lots of different lump brands.
RE: Grates - If you're going to burn lump, get a second grate for the bottom. Stack the two grates at right-angles. This makes the "holes" smaller, so that the lump does not fall-through, and it makes it a little harder for the lump to clog-up the air holes at the bottom. Remember: Fire = Fuel, Air, & Heat
You gotta' keep it breathing.
RE: STIR YOUR COALS - I keep a 3-foot chunk of conduit, with the last foot of it bent. I use it to stir the coals when the heat seems to be diminishing. Particularly with Cowboy, I sometimes get hot-spots within my fire, that are a bit reluctant to spread to adjacent un-burnt coals. Stirring the coals helps to minimize this. (I usually do this after about 2-3 hours, and about once every 90 minutes, until I notice that I need to add some more charcoal.)
Hey, this aint the bible, but it might help you.