As a
travel agent, I of course recomend using a TA!
But really, WDW is possible to plan yourself, and many find it half the fun of the trip. BUT it can be VERY time consuming, so if you don't have a lot of free time, a TA may be the way to go.
As far as price is concerend, TA's don't normally do better than you can on your own, but it won't cost you more, either (if you have a good agent!). You may want to at least check on airline tickets with an agent, and then compare what you find on the web. I've found that lately I'm meeting or beating the web fares.
If you do go the TA route, make sure your agent has been to WDW, preferably in the last 2 or 3 years, and if they are a College of Knolledge grad (CoK is a Disney run TA education course) that's even better. Ask lots of questions!!! And answer the agent's questions as completely and honestly as you can. Give them your budget, and be honest with the number. A good agent should give you at least two options when they come back with a quote (unless you specifiy a specific resort, that is!).
Be carefull with the agent you choose. There are many out there that don't know much about WDW. They could be great agents, but WDW is so complex that the agent really needs to know the lay of the land, and that means that they should have traveled there at least once, and preferable several times.
Compare the Dream Maker package to just hotel and park hopper passes separately, the DM package is usually more, but not always, especially if you go while the 7 for 5 deal is valid.
Also, it sounds like you may have enough people for a Grand Gathering. GG's are for parties of 8 or more, and Disney has coordinators that can help you (and/or your TA) plan events and outings as a family and other details, a good TA can help with this too if you don't have enough people for a GG. Also, it gives you a 'stick' to wave at the other party members if they drag their feet on getting you info or money. "The travel agent must have this info/money/whatever by such and such a date." It make the TA look like they're the one doing the nagging and not you!
Either way, you'll have a great trip! Good luck!