We seldom make the parks early so these are obversations mainly from an afternoon to early evening perspective. Also, our daughter is ambulatory (Down Syndrome) although she can have melt downs and health issues with being in the parks too long in one day or waiting in lines too long.
How we use the combination differs among the parks and can differ on any given trip to a park. You can modify the three FP+ times suggested to you after you lock them in online but you have to do each one individually and it takes a long time but we go through that process. Also, for most stage or movie type shows like Philarmagic at MK and Little Mermaid at Studios you don't need to use a FP+. They have just treated the
DAS card like Fastpasses like they did under the old system. Here is one system we have followed, which obviously can be modified:
Epcot: the major problem with Epcot is that you cannot get an FP+ for both Test Track and Soarin or a character meet the same day. Those are actually the only three things you really need FP+ or DAS for in the afternoon or evening. Spaceship Earth often has little or no line much of the afternoon. Energy is easy to get into, as is Captain EO and Journey. Mars is also usually short. The Nemo ride at Seas is usually fairly short in the afternoon although you might consider it as one to use an FP+ on. Also in the afternoon, you can usually get into the Turtle show and they have treated the DAS simply as a fastpass there.
Thus, if we want to do Test Track and Soarin the same day, we are likely to reserve Test Track with an FP+. Soarin has Land and the Lion King environmental movie in the same building and when we go there we use the DAS to get a time for Soarin and then do the others and often have lunch there. We may use one of the FP+ for Land too just in case.
Studios: You cannot get both RnR and Toy Story with FP+ the same day. Those and Tower, Star Tours, and possibly Great Movie Ride are really the only attractions you need FP+ since Beauty and Mermaid treat your DAS as a fastpass without getting a time and other things are usually easy to get in. If we are doing just a day, we use FP+ on Tower, Toy Story and Star Tours. We arrange the times so that when we go to Tower, one of us first gets a DAS time for RnR and then after Tower usually go there. Then we will do Beauty, after which we go to Toy Story with a time shortly after Beauty and one of us may stop at Great Movie first and get a DAS time, so we can do it after Toy Story. Star Tours FP time is generally later and we do some of the others before or after Star Tours usually without using FP+ or DAS.
Animal Kingdom: since they treat the DAS essentially as a pass to entry at the Nemo show you do not need to use an FP+ on it. We will usually get FP+ for Dinosaur, Everest and Safari.We arrange those times so we do Dinosaur first, then often Nemo, then Everest. Then we get a DAS time for Kali and may go to Safari first. We usually do Tough to be a Bug late because it usually has no line then. We sometimes do the bird show while waiting for our DAS time for Kali but you don't need anything to get in there.
Magic Kingdom: Having only three FP+ for MK is grounds for executing the "Suits" who created that rule. it is just too few for all the attractions there that can have long standby lines. Even with DAS MK is going to take two days to get all the key rides. For us it is usually two days and sometimes three because it is daughter's favorite park and she cannot physically do it all in one day. We sort of view it as left side and the right side. One day we will do Adventureland, Liberty Square, and Fontierland; the other Fantasyland, Tomorrowland and Storybook Circus. She does not care for Space Mountain, Astro Orbiter, or Stich so we don't use anything on those.. On the left side day we will get FP+ for Pirates, Railroad, and Mansion, with Railroad right after the FP time for Pirates and Mansion Little later. We do Tiki first which has no line in the afternoon but before doing so we get a DAS time for Jungle Cruise. If she wants to do Alladin, we get a DAS time for that after doing Jungle Cruise and and then go to Pirates and come back? Then we do the Railroad but get a DAS time before doing so for Splash Mountain; after Splash we do Country Bear (no need to use anything) and Presidents (if I can convince her to go), and then late in the afternoon or even early evening before dinner we schedule Mansion.
When doing the right side, we usually get FP+ for Dumbo, Pooh and Pirates. We then do Tomorrowland first, doing the monster show for which they treat the DAS like a fastpass and you usually don't even need it in the afternoon anyway. Before doing Monster we get a DAS for Buzz. Then after or before doing that we often do Carousel of Progress. Those are the only things she likes in Tomorrowland. Then over to Circus for Dumbo but get a DAS time for Barnstormer unless it looks easy to get on (many times in the afternoon it is).
Then we go to the Mad Tea Party and get a DAS time if one is needed, then to Pooh with FP+, then to Journey of the Little Mermaid; if line is long we may stop at one of the food and drink places after getting a DAS time. Then we get a DAS time for Small World if needed (often it is not). If it is we go do Pan first with an FP+, then Small World, then the Carousel for which an FP or DAS time is seldom needed, and then Philarmagic for which DAS acts like a fastpass and it usually does not need any late afternoon anyway. Note, we will sometimes also reserve a character meet with FP+ rather than Pan, and then get a DAS time for Pan. Obviously, once the Dwarfs mine ride is available we likely will use an FP+ or DAS time on it.
