I see you have made your decision to go to the Beach Club. I think you made the right decision. I too have a teenage boy, and he loves Stormalong Bay, and will opt out of a park day just to swim. We have to pull him out for dinner, and he doesn't leave until the lifeguards close the pool in the evening. In my opinion, the pool slide at Stormalong Bay is the best slide of the resort pools, and we've done them all. The only slide on property that can beat it is at Blizzard Beach. If all the action at Stormalong Bay is too much, the adults can just walk around to the quiet pool, for a relaxing nap, get some sun, or to read a book in a more serene atmosphere.
I have stayed at both the Poly and Beach Club resorts. The Poly is great for it's convenience to the MK, but as your interest is EPCOT, the Beach Club is the resort for you. You can get up and walk to EPCOT, which is nice in the morning and evening. The Yachtsman Steakhouse is a great place for the adults to have a private dinner, while the kids explore the activities of the boardwalk shops and arcades. There is also a wonderful ice cream shop called Beaches & Cream, where you can pick up a really good hamburger or other soda shop items, and of course their signature Kitchen Sink Dessert with I think it's about 12 scoups of ice cream and everything else you could imagine, that's served in a replica of a kitchen sink. The Beach Club also serves a wonderful character breakfast. I'm sure you will be glad you chose the Beach Club Resort.
Have a safe and fun filled vacation.