I would also say that if Princesses are a MUST HAVE that you should look into a character meal that includes then. Akershus seems popular and has a lot of princesses. Also popular is Cinderella's Royal Table, but it's pretty expensive and in high demand. If you can't wrangle it into the budget, then lock down your Fastpass + on some princesses (you'll read about it. Don't worry). However, I'm an adult and even I find character meals perfectly charming.
For parks, I'd say you'll need 2 days in Magic Kingdom (MK) alone since your kids are all on the younger end. Animal Kingdom (AK) if your kids like animals and dinosaurs. EPCOT if you want them to have a taste of other cultures without having to leave the country. They also have things explaining energy, machines, sea exhibits... And things for your kids to do all over the place.
I've paged through some beginner books and some of them are really excessively long. I'd recommend that if you are good at skimming, that you do that first and stop any time you see anything that seems interesting. Sometimes there are simply long lists, or prices have changed since publication. In these cases, skip the list unless it is something you want, and double check prices for things that interest you either here, easywdw, or allears. Those are my 3 favorite sites for up to date things. If you are a quick reader or if you just really want to know every little thing, go ahead and read the full book!
Keep in mind that some of the strategies found in them are biased as to efficacy, however, or what is "good for" your family.
As for strollers... You do have a second adult, correct? Strollers are unwieldy and can be a pain to stash, but if your kids aren't used to walking long distances it might be a must. If you or your spouse are very fit and regularly hike or similar, you should be fine with carrying the baby instead of using a stroller. Otherwise it might become a burden in the long run, unless you alternate the baby in stroller while another kid walks. Keep in mind that buses require that you fold a stroller, so a quick collapsing one will make for less awkward moments.
For a quick prep, since you have a hotel chosen, I'd say skip reading the hotel stuff for now. Instead, skim through restaurants you might want to make a reservation for, then how Fastpasses work, then rides or experiences you want to Fastpass, then other things. This way you can be ready to lock down reservations and the like ASAP, and clear up any worries you have here. You can also have maximum time to create backup plans in case you get confused by the site or how to reserve things. People here can help you with more specifics regarding a day plan, how to wing it, best times for things, etc. after you have some preliminary knowledge. It is also helpful to reflect on what kind of vacationers your family is. Do you like to stay up late or wake up early? Does the whole family hit that afternoon slump? Does anyone need regular snacks, or hate loud noises? Do you all get cranky if one person is cranky? Etc.
Best of luck, and I hope to see you around here while you research! I'm going in October too, and I'm so excited!
