I don't agree with the "do everything you can" approach (although I have done it myself many times). The reality is, you're not going to do/see everything in one trip.
And as others have said, one person's "must-do" is another person's waste of time. I think it's also smart to think about what are overall priorities for you. For some people, food is a really big deal. For others, it's fuel, something to grab quickly and then move on to the next show or ride. If food is a big deal, look at the menus that you can see online and get a sense of a couple of places you'd like to try. If it's not a big deal for you, anticipate that you'll be eating some burgers or sandwiches from the counter service places (many of which are really good). Disney does have good restaurants but so does the rest of the world, and the rest of the world doesn't have Splash Mountain, so if forced, I'd pick SM. But that's my priority.
Are the parades and fireworks important for you? For some people, they are absolutely essential. You will have to deal with crowds and standing around waiting if you want "the perfect spot" to see parades and fireworks. Is it worth it? Maybe you'd rather use that time to go on one of the busier rides. Only you have an idea of what you want to do.
Attractions - is this a priority? What about rides versus shows? Personally, shows were never a priority for me until probably my fifth or sixth trip. Up to that point I prioritized the rides over everything else. Now, I enjoy the change of pace and the relaxation that comes with taking in a show. Again, only you know what's a priority.
Most of all, I would say to walk around and let some things happen naturally. You will stumble across great stuff even if you don't have a schedule. Don't run across the park trying desperately to keep up with fastpass appointments. I'm repeating myself, but it's true: you can't possibly do everything, but that's okay. I wouldn't approach it as a list of things to cross off; it's a holiday. Walk into the Magic Kingdom and see where the day takes you.