1) I ditched the cheap grill and went to a pizza pan. Holes should work as well
2) Risers on the outside of the grill will reduce airflow. I don't use them.
3) I use the bung hole with a stack. No issues on low and slow, will cause a hot spot on a hot run.
My biggest problem was damp charcoal. I fear a water bath would cause same issues. Lots of energy is used to evaporate water. Hard to get temp up when you are evaporating water. Once water is gone, you get a spike/runaway. I could tell the difference from a fresh bag of lump to one that was oppened and left in my garage for a couple weeks.
I put a Guru on and never looked back.