I think the answer to your question depends on how much you know about WDW in general. You said it was your first stay on property, but perhaps you have been on trips there before...
If so, and you feel you know a fair amount about how the tickets work, you have read lots of books or spend a ton of time reading these boards, then you are most likely just as knowledgeable (if not more) than some of the travel agents.
We used Small World vacations for our first trip because I was paranoid I would miss something in the planning. Although our agent was nice and helpful, I felt she did not always get back to me quickly when I contacted her. I also realized I knew as much if not more than she did from all my research - but I am a planner and very obsessive about finding out what I can when I go somewhere new. After that first trip I planned the next two on my own and have never regretted it.
Good luck in whatever you decide!