Whats the best plugin or app to manage users of Multi-sites by outsourced staff?

I would like to assign two or three oursourced staff to administer the multisites. Im anticipating 10000 members in the next 3 months after launch.
I would like to assign or designate various WP responsibilities and also be able to have a log of their activities. Especially Support and Help desk ones.
BTW, are there applications already available to use that are in production.