A Disney vacation can be much more complicated than many other types of vacations; mostly because there are so many options available. We always book our own trips, booking and buying each element separately. We don't book packages simply because we don't like the
DDP, and without the DDP, a package is unnecessary. And we never book our flights as part of the package if we can avoid it.
Unless you have the time to research the different resorts, discount offers, ticket types, etc yourself, then I'd recommend a TA.
But ONLY if that TA is a Disney Specialist. Yes, there are entire agencies that specialize in Disney vacations.
But if you have the time, you can learn everything you need to know on your own. I would suggest a good place to start is with a good guidebook. 2 that are excellent are The Easy Guide to Your First WDW Visit, and the Unofficial Guide to WDW. There are also very good websites, like Easywdw.com, your first visit.net, touringplans.com, and Mousesavers.com, just to name a few.