I've never seen an estimate for the average size or range of a crew that was based on anything substantial. The number 10 may originate from "decina." Some crews may have that many, others more, others less.

Associates fit both descriptions - ones that work directly for a soldier or captain. Others that work with the mob at times in an ongoing capacity.

The gang thing is not as much of an issue as you might think. Different criminal circles in different areas with different rackets. Only occasional crossover.

And it's misleading to say a crew "controls crime" in a given area. It's not like every mugger, car thief, burglar, or con man is kicking back tribute. Sure, there are examples of a crew who has maintained tight control of the drug trade in certain neighborhoods. But the mob is, and has been for many years, more about business territory than just geographic territory. This union local belongs to one crew. This garbage company belongs to another. Etc.