I'd try again for FoP starting a day or two before the day you expect to be in AK, same for the Mine Train and your MK day(s). One thing I found when I had a single day is that if I booked all three available FP+ at Animal Kingdom that morning, I was more likely to get a scheduling conflict error if I tried to search for FoP to add as a third. I ended up just booking Na'vi that morning and leaving the other two slots open. I never managed to get a FoP FP, but had great success showing up an hour before the park opened and going straight into the mob line for it. Plenty of people will also tell you to go right before park closing, as the end of day wait times are usually exaggerated.
I can't really speak to prioritizing FP+ off my head too well, especially when I don't know what's a higher priority for you in general. If you want to ride Peter Pan, though, you'll need to either go at rope drop or use a FP to avoid a big line; I mention that because I don't find that ride's huge popularity intuitive when it's so old and relatively low-tech.
The big thing that really, really worked for me was actively searching and re-searching for FP+ throughout the day while I was in the parks. Whenever you're in line or on a bus, check for FP+ availability. If you see a FP for the next ride you want but the time is later in the day than you were looking for, book that FP anyway. Then use the "Modify FP" button to keep searching for earlier times (it's quicker than running a full FP search every time). I was able to book multiple headliners and then move them up to an earlier time slot that way.