Dirt's a fact of life in an unsealed environment. Lightly sand it out and move on.
As far as the W&G goes, if it's not flashed off you may end up with a whole lot of craters. Then you gotta redo it. Remember Barry's mantra "Slower is faster"
1.2/1.3 usually for base and 1.3/1.4 for clear. There's been several posts about how the new SATAs are actually a step bigger than what is shown.
Follow Barry's gun set up and you'll get it figured out.