Whether or not to buy the dining plan is a personal choice based on your budget and eating habits. It's perfectly fine to do whichever works best for your family. Many of the moms on the Panel always use the dining plan, but for a variety of reasons, I never have.
On the other hand, whether or not you use the dining plan, you do need to make restaurant reservations. You don't say when you are traveling, but during even the moderately busy times of the year you will have difficulty eating at table service restaurants without advance dining reservations. As a first step, I would take a look at the
Dining Finder on the WDW website to see what your options are. Then take a look at the park calendars for the dates of your trip to get a rough idea of which park you want to be on which day. Then, call Disney Dining at 407-WDW-DINE to make some reservations. Even if you need to change your plans later, at least with some reservations made you will have more options.
Hope this helps.