Hi, Clayton! There are special rates for groups that book ten or more rooms at the Walt Disney World resorts, and larger groups may also qualify for discounted tickets, special events or experiences, plus a group services manager that will be assigned to help you coordinate everything.
You can find more information on planning for a large group by visiting
Disney For Groups.
As for whether or not it's better to go through a travel agent, I think that would be personal preference. I would have complete faith in Walt Disney World to help me get through everything, but some people like the face to face interaction they get with a travel agent. There are many awesome agents, some who will even do things like coordinate dining reservations and group activities, but you can do that through Disney as well. It really comes down to what you will be most comfortable with.
I hope your upcoming vacation is absolutely magical!