To the first, these things tend to spread throughout the team over time, so by the end everybody will be using those 40 hotkeys if they're indeed helpful. If some people like them and others don't, they'll figure out how to resolve the difference with the least possible amount of fuss. With regard to color schemes, I've never seen a dispute over those, personally. People may come to the table with different preferences, but over time those also resolve one way or another.

In my experience, severe competency issues are actually /better/ dealt with via pair programming than the alternative: pairing forces their competency issues to the surface, and can be dealt with more easily. Personality conflicts can be worked through, or the team can be changed up. When things like that don't work out, the worst thing you can do is make too big a deal out of it...reconfigure the team one way or another and move on.