One thing I would add is that if you get FD and are staying at a value it is usually the Quick Service Dining Plan (QSDP) not the DDP. If you get FD and want the DDP you would have to upgrade to a Moderate. At least, this is what I have read on this board.
Another thing to consider, if you really wanted the DDP instead of just quick Service, you can 'buy up'. For example, you're staying at Pop Century during a
free dining promo. That includes the QSDP. You really want to do a couple character meals and sit down meals that week, so you want to buy-up to the regular dining plan. that cost (with current plan prices) would be $18.05/day for each adult and $3.20/day per child for a total of $42.50/day or $340 for an 8 night stay. PLUS at least another $140-160 in tips. Or about $500 total.
That might not seem so bad, but then you have to remember that you are now obligated to 8 sit down meals. To get your 'money's worth' out of the plan, you want each of those sit down meals to be worth the value of a quick service meal PLUS the price difference. Some restaurants are better values on the plan than others. If you absolutely must have a sit down dinner every night, buying-up is your best option. If you don't mind counter service for most dinners and just need one character meal and 1 or 2 other sit down meals, you'll save money buy paying for those out of pocket.
For example, you want a character meal and manage to get a ressie for Cinderella's Royal Table (price there includes tip!) Your total for that would be $215.82. Then you want one nice quiet family dinner and decide to do Ohana, that would total $120.31 +tip (so, for me, it would be $145). Those two would total $360.82. You decide you still have some room left in the budget and squeeze in a character breakfast at Crystal Palace (breakfasts are cheaper!) for $72+15tip ($87 total). That takes your total to about $448, still less than "buying up", and, remember, you have the 3 meal credits left that you would have used on those meals if you'd bought up, so you are actually getting 19 meals (16 CS, 3 TS) for less than the price of 16 (8CS, 8TS).
Your budget is incredibly tight, and the only way you'll stay close to it is if you get free dining. That said, if you keep an eye out for the discounts and plan really well, then you may come in under $2500. I'd also look into other discounts available like stacking the YES program with a room only discount and paying out of pocket for food (Although free dining would beat that hands-down).