If you are going to be at the park for 2 1/2 days (and able to hit rope drop at least twice), I would suggest cutting the park more or less in half and splitting up your attack on the busy atttractions on two different days if at all possible. We typically do a Fantasyland/ Tomorrowland (and former Toontown) and an Adventureland/ Frontierland/ Libertysquare combo, but it doesn't have to be that way.
Dumbo would definitely be a priority. The lines are long, move slow, and there is no fast pass available. The other ride I've seen with horrendous lines all day long is Peter Pan. It does have FP though, but they do run out so get one early.
Other priorities would include: Space Mountain, Splash Mountain, BTMRR - they all have fast pass, so I would take advantage of that whenever possible
Also, the Indy Speedway and the Astro Orbiter get really long (slow moving) lines so you might want to hit those early if your kids are interested in doing them. I can usually get away with doing Dumbo OR Astro Orbiter, but they never want to skip that darn speedway!
I would imagine that Merida will have a really long line like Rapunzel as soon as the movie comes out and all the kids know who she is. Not sure what Tiana's line is like.
I would also ask your 4 year old what she thinks you are going to do that day and make sure to incorporate it into the 1st day plans to avoid any meltdowns. I've often been surprised at what my kids say is their number one priority. One year, I thought DD would be all about the princesses, turned out Pluto and was at the top of her list of characters she thought she was going to meet.
And, don't forget about baby swap. This will allow you to maximize those FP's.
Lastly, you may want to check out easywdw.com There is great info. there about when to meet characters to avoid major lines, etc...
