I don't know that I've ever ridden everything at MK in a single day--I may have done it (or come close) and not realized since I've never set it up as a goal. That being said, a long day like that should give you more than enough time.
If you're able to get your FP+ for Peter Pan and SDMT, that knocks out the two tough ones in Fantasyland, so that's a solid plan--and with Haunted Mansion relatively close by, that keeps your first three FP+ pretty nicely clustered. I'd hit either Space Mountain or Big Thunder at rope drop, understanding (unfortunately) that you're basically running to the back or side of the park for one ride on a mountain before heading back to Crystal Palace for breakfast--you might be able to sneak more attractions in during that hour, but I would go in with the assumption that you're only doing one thing before breakfast. As the previous poster pointed out, too, if you move your breakfast to later in the morning you'll have more prime morning time; if your ADR was at 9:00 or later you ought to be able to knock out all of, say, Tomorrowland without needing FP+.
How big is your party? As a solo traveler my strategy to tackle this would consist of playing the refresh game on the
MDE app to move up FP+ and snag more of them throughout the day. As your party gets larger, though, that gets harder to accomplish--but it's still worth trying. Say you have the following FP+ set up ahead of time:
9:30-10:30 - Peter Pan's Flight
10:45-11:45 - SDMT
12:30-1:30 - Haunted Mansion
Say you tap in for your Peter Pan FP+ at 9:45. Once that FP+ has been used, it's no longer sitting on your account preventing you from booking anything before 10:35. Get on MDE while you're in the queue and hit the button to edit your SDMT FP+, and keep refreshing until it gives you an earlier time--with any luck, you'll get an earlier FP+ window and will be able to go straight to SDMT immediately after leaving Peter Pan. Do that again with HM, and once those three are all used, keep working to book more FP+ throughout the day. I found it's quickest/easiest to book literally any FP+ you're able to get for the ride you want and then modify the time, so if you're looking for Big Thunder at 1:00 and the earliest available is 6:00, book it anyway and just keep refreshing the "modify" option until you get an earlier window. And then any time you're between FP+ because you weren't able to move a window up enough, use that time to ride things that have smaller lines and higher capacity like the Carousel of Progress, People Mover, etc.