Browse around the Theme Parks board and you'll get a lot of planning advice. I also recommend the Unofficial Guide to Walt Disney World, and its companion site at
www.touringplans.com.
The way I read you posts it sounds like this may be your first family vacation to Disney World EVER. If so, congrats on having the faith to buy into
DVC.
I will offer one bit of general advice. I don't know how often, if ever, you have vacationed as a family in the past. One really great rule to remember is that your kids--particularly the infant and 4yo--won't take kindly to having their normal routine disrupted. Whenever possible, I always suggest maintaining normal eating and sleeping times, including both afternoon naps and nightly bedtime. If you try to disrupt those schedules too much, you're just asking for grumpy kids and unwanted meltdowns.
We have a 2yo daughter and a 4yo son. Our daughter is a stroller sleeper. She's been to WDW twice, and had no qualms about drifting-off in the stroller or even when being held on a ride.
Our son is a different story--he won't sleep unless he's in a comfortable bed in a dark room. Keeping him up all day isn't a good option, so a mid-day nap break is a must.
So, apply that logic to your family and plan accordingly. In September the weather will be HOT, HUMID and often rainy (it's also hurricane season, so you get a lot of storm fronts from the gulf and Atlantic.) As parents, we may find we value our mid-day break as much as the kids. Just being able to change into a fresh set of clothes is reason enough for me.
If your 7yos don't won't to be in the room, have one parent take them to the pool, Hospitality House or even Downtown Disney while the other stays behind with the younger kids.
Regarding Stormalong Bay, the only comment I'll offer is that many parents find it hard to keep an eye on the kids given the enormous size of the complex. If you're looking for a place to lounge a bit while being confident that your kids are right in front of you and safe, SAB is probably not a great choice. At most of the smaller resort pools you can sit on the sideline but still have all of the action right in front of you. The Beach Club does have a "Quiet Pool" that is much smaller in scope, but it doesn't have a slide for the kids.
Good luck with your planning.