Thought I would come back and answer my own questions, since I'm back (went on 8/31 with premium package).
1.) They had us park our strollers upon entering the package area for the parade. We did not sit in the children's section, just sat on the ground behind the rope in the regular section and visited and enjoyed our treats in the shade. Stood up and held kids for the parade. Then walked up after the parade to a close view of the stage show. Worked out well, except for how quickly those Mickey bars melt!
2.) They also had us park the strollers upon entering the dessert party. We found a low table in the front, so the toddlers could stand and reach things (though we had to be careful of our adult drinks!) Our kids were dancing and having a good time, but we saw other families that had strollers near their tables. I'm guessing maybe they were allowed if the kid was falling asleep?

We moved before the fireworks. We got the strollers and moved to the very back of the area, next to a treat station. Good view, we were happy - and easier to get out afterwards (though crowds were CRAZY!)
3.) I was given two sing-along tickets at package check-in, even after confirming that my daughter was under 3. So, I think they would get their own seat. However, I was on the slowest boat in the world back from our afternoon at Epcot and was late for our 7pm sing-along.

After running through DHS and explaining to 4 CMs that I was late by a few minutes, they let me in and put me in the back row, right section leftmost seat. My daughter on my lap. There was a large column blocking our view of the storytellers much of the time, but we had a great view of the sign language interpreters, which was fun to watch. Kristoff was blocked when he first came on, but he eventually moved where we could see him. We still enjoyed, but I'm sure it would have been nice to be closer. FYI, they told me that they fill in the unused package seats before the show, which is why we had to sit in back.
Hope this helps someone! We had a really good time.