There are two types of people in this world: Those who love planning a WDW vacation, and those who don't
I think the key is not being super ridged in your planning. I always visit for three weeks, so yes, pretty tough to know in the third week of the holiday what I want to be doing. But in my experience, I have almost always been able to change things the night before - even hard to get dining reservations as other people also change their plans. So I just book what I think I might want and then change on the fly if needed.
My approach, which I find fairly stress free is this:-
An excel spreadsheet, with a column for each day of the holiday (honestly, for a three week vacation, this is a must, even with non-Disney vacations to keep track of where you're supposed to be). I reuse this same spreadsheet template each year (and start with the previous years plan as a base). And along the first row of the spreadsheet, each day I decide which park I want to visit... It roughly goes like this: Magic Kingdom on the first full day, then each subsequent day a different park until I've visited each one. Then for week 2 and 3, I largely just cycle through them, with the parks I like most having more frequent repeats. I then build my reservations on top of this. So if I'm at Animal Kingdom, I know I'll want a Yak and Yeti reservation, so I note that down. I put in all the places I'd like to make sure I hit up. Once I've added all the restaurants which I really want to visit, I then fill in any gaps as needed. I roughly look to eat at around the same times each day, an early'ish lunch and a late'ish dinner. From this point, I know roughly where I'm going to be and at what time, so its fairly easy to know what time to book fast passes. I always try and make sure I schedule FPs *before* a dining reservation and not after, so I'm not rushed through my meal.
I do this planning in advance of the reservation windows opening - so when it opens, I just work through my list relatively stress free.. I always use a bit of experience, so for example, I don't try and book Flight of Passage in the first week of my trip, because its available to almost everyone. I take advantage of the 60+10 rule (if you have a resort reservation, at the 60 day mark, you can book as far out as 70 days). Proportionally, relatively few on-site guests stay 10 days, so its much easier to get the "hot ticket" items towards the end of that 10 day window as far fewer people have access to reservations that far out. If something is not available as I work through my list, I just pick a second choice, and come back to it later. I have never failed in getting what I want out of the full three week trips I've done. Quite often by the third week, I've decided I don't want to do certain things, so I just cancel. Better to have the reservation than not - so if you don't know for sure, just book it and cancel closer to the time.
So basically, relax, take your time and try and have fun with it. At least for now, one extra complication, FastPasses, have gone away so one less thing to worry about!
