Those are terribly hard things to measure with metrics. Please for the love of all things beautiful may no one list out "number of bugs" as something they measure.

A lot of this gets covered in retrospectives. Making sure that you don't repeat similar mistakes over and over again and that the team is evolving rather than becoming static. I tend to focus more on how well we hit our goals (including business goals) so that will include things like, "Are we getting better at estimates?" It could also informally include, are Dev1 and Dev2 arguing less and communicating better?

I usually leave metrics to the product side. Find your version of Facebook's "7 friends in 10 days"