As for you last question. It's not so much a note that is out of key that sticks out like a sore thumb. But a tone in the melody you want to play has a bad melodic quality. Usually referred to as bad phrasing. Also playing notes that may seem out of key is not a bad thing. Your right it sticks out like a sore thumb, but that can be good. Why? Because it immediately attracts the ear, which combats monotony. Notes out of key provoke interest. I'm not saying do this, because that is not the point. The point is having good melodic phrasing regardless of the notes. There are a ton of scales out there that have notes out of key, yet they sound good.
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.