I don't know where to begin and I've been visiting several times a year since 1992, so I can't begin to imagine your dilemma!
The first thing to mention is that you should just chill out and be prepared to enjoy every choice. You can't possibly experience every dining option in one trip (hell, we haven't experienced them all in over 200 days!), so don't torture yourselves by imagining you might be missing out.
On the whole, the resort restuarants beat the park restaurants hands-down. That said, that won't always fit with your itinerary and, anyway, I think it's nice to get a mix of both.
I assume you'll be visiting all 4 parks and, as you're asking about
DDP, that you'll be staying onsite. You've already identified full dining options at MGM and Epcot.
For a first-timer, I would recommend the following:
MK - Peco's Bill (Counter). Great burgers, chilli-cheese fries and fixins bar. Crystal Palace (Buffet). Beautiful space. Good character interaction (Pooh and friends). Very popular, so you definitely need to book. Go for a later breakfast or lunch and that way you wil get more attention from the characters as they wind down for the next session.
Epcot - You've already selected Coral Reef as your full-service choice. It's a tad over-priced in my opinion, but quite nice nonetheless. Trust your instincts - as I say, you can't possibly do it all. Le Cellier is another good choice. For counter service, consider Cantina de San Angel (Mexico) or the new Season food court at The Land.
AK - for me, this is the most disappointing of all the park dining options. I'm probably not the best person to advise on this as I think they're all dire. We always end up at the Rainforest Cafe. It's definitely a 'love it or hate it' place. I don't think it deserves the bad reviews. We've always found the food to be fresh and plentiful, and the theming is quite cool. It does always seem to be a bit on the expensive side, but the portions are huge, so don't over order.
MGM - The full-service options are better than the counter options. The ABC Commissary (Counter) is acceptable. The 50s PTC is fun - good choice. We also enjoy Mama Melrose and Brown Derby.
Where are you staying? Do you enjoy fine dining? There are so many good options at the resorts. Caifornia Grill (Contemporary), V&As, Citricos (Grand Floridian), Flying Fish Cafe (BoardWalk), Artist Point (Wilderness Lodge), Jiko (Animal Kingdom Lodge), bluezoo (Dolphin). They all afford a great opportunity to check out the resorts, too. Then there are loads of fun options at the resorts - ESPN, Whispering Canyon, 'Ohana, Boma ...