Help! I'm trying to figure out a plan for fast passes for Magic Kingdom. I need to know the best plan for when we arrive at rope drop. Where should we go, and what should we ride first before FP? My DD has a BBB appointment at 1pm. After that we want to meet the princesses. Is a FP really needed? Probably with Elena possibly there? Help me maximize my time. Please!
I pick my FPPs based on the question "Which rides would I be the most upset about if I didn't get a chance to ride them". For me, Splash and BTMRR are always on that list and the 3rd varies, but is usually SM or 7DMT. I typically make my FPPs for the afternoon (at least not before 11:00 AM) as that is when the park is most crowded. If you are staying on-site, I highly recommend using AM EMH at the MK; that combined with the first 2 hours after general admission RD can REALLY boost the number of attractions that you get to see. But whatever strategy you use for selecting FPPs, hit the other headliners right at RD. If you want to ride PP or 7DMT, and they're not one of your FPPs, I'd recommend going there first because those lines build very quickly and stays long all day. I never do M&Gs, so I can't really comment on the necessity of FPPs for those.
In our experience, we have got FPP for the princesses and that has saved us a lot of time, particularly for Rapunzel as Fairytale Hall is her only M&G, and particularly if you are meeting in the middle of the day (and not at RD or last thing at night). Like you say, Elena will be very popular too. There's lots of great info on Kenny the Pirates website regarding meet and greets so you could have a look on there (if you haven't already). I would be interested to hear others experiences of waiting in line for princesses.
I would recommend doing a personalized touring plan for Magic Kingdom for your dates, optimize it and let it tell you which attractions or character meets would be best to use a fast pass. I tend to do my fast passes earlier in the day, around 10, 11, and noon in order to take advantage of the opportunity to pick up a fourth+ additional fast pass. Keep in mind which fast passes go quickly. In my experience these tend to be 7DMT, PP, and character meet and greets, so if the meets are important to you it might be to your advantage to use fast passes for those as it will save you a ton of time that you would otherwise stand in line.
I also would recommend Kenny the Pirate's site for more detailed character information.