How to put together a great Agile team...

How to Balance the Size and Skills of Your Agile Team
http://my.gartner.com/resources/220700/220700/how_to_balance_the_size_and__220700.pdf?li=1

Gartner did a great job in showing typical skills of Agile software development teams. They've looked at a number of disciplines and drew conclusions that, e.g.:
Master (not automatically ScrumMaster):

Experience: Five to eight years

Productivity: Very high, 18 to 25 FPs per staff month

They also have tables that show how the teams are usually composed and what it might mean.

Interesting reading

@MiroslawStaron