Originally Posted by PAR

For me this would depend on how may sites,
What type of sites,
The type of backend and billing setup,
Number and timeline on updates,
How much effort will be put in webmaster traffic vs inhouse traffic generation vs traffic buying,
Expected release rate of new sites,
Webmaster marketing tools, (depending on what they are they will need updates and support)

You can have 2 companies, both with say 20 sites...
Depending on the setup company "A" can have 3 staff Company "B" 120 staff...

So its not really an answerable question...