24/7 coverage of report handling is next to impossible with volunteers and I don't know if this group has the budget to pay moderators. But in my experience as an admin on another website it is sufficient to take appropriate action within 24 hours.
A flagging system can be helpful, but no action should be taken without a review by the team. Proxy blocking could help too, but doesn't prevent abuse completely. That's only part of the solution at most.
I believe that a properly trained and supervised taskforce of volunteers is the best approach, because that way you aren't limited by budget to hire enough people to keep up with the work.