Hi Allison,
Wow! A 14 night Disney vacation sounds heavenly. I actually would recommend splitting your stay between the two resorts.
The
Polynesian Resort is in a fabulous location on the monorail and is close to the Magic Kingdom and Epcot. The
Beach Club is my favorite Deluxe Resort. It is walking distance from Epcot and is a relaxing boat ride away from Hollywood Studios. While they are both beautiful resorts, they are very different from each other. They're both highly themed. The Beach Club has Stormalong Bay, an absolutely amazing swimming pool complete with a sand bottom, lazy river, whirling waters and slide. I recommend that you spend a week in each one. It'll be like having 2 separate vacations. I'd do the Polynesian first, and then end at the Beach Club when you may be ready for some relaxing pool days.
As far as your Disney Dining Plan, you'll need to be on two different plans (one for each stay). The only way this will affect anything is that you'll need to use up all of your credits from the first stay by midnight of the day that you check out of one resort. You'll get a whole new set of credits when you check into the second one.
One of my goals is to stay in every single Disney resort. This November, I'll be crossing 4 off my list. My family is going for 11 nights and we're switching that much. It keeps things interesting and allows us to experience more of Disney that way. Moving is quite easy. You'll just pack up your bags, give them to Bell Services and they'll move it all for you. When you get to your new resort, your bags will be waiting for you.
Hope this helps. Please let me know if I can assist you further.
Have a wonderful vacation,
Kaylene