You have it backwards!!!
It should be the Kona Cafe for breakfast! Treat yourself to the real Kona coffee in the special pot and the "Tonga toast" (my DH special favorite) and you will hit those parks at warp speed for the day. Nothing else needs to be said on that. No need for lunch, well maybe just an ice cream to tide you over.
(Drink plenty of water though, ALWAYS at wdw so that the sun and heat do not make that shimmering pavement come up and smack you on the face. It is amazing how fast that heat exhaustion can get to you- It got me for the first time last year at EPCOT! It frightened me.)
Make PS's for a fairly early seating (5:30 - 7:00 pm) at Boma as they tend to run a little behind with there seatings and this sometimes gets worse as the night progresses.
My theory is that people just can't tear themselves away from that doggone dessert table!
Boma is our favorite buffet- it gets a bad rap for having "way out African foods" from some posters here and I just have to scratch my head. Yes some of the selections were new to us, but try it, you may be pleasantly surprised! I know we were. Even our kids liked trying the new things. They were visually appealing and tasty and the aromas are fantastic. Lots of very friendly chefs right on the otherside of the line smiling and just waiting for friendly people to take the time and ask them about the dishes. They really seem to genuinely enjoy telling you about it. A brief description is posted above each and every offering if you don't care to talk to strangers.
Even if you are the pickiest person on earth they have more than most other buffets have which would be called "normal stuff". The best hand carved prime rib on site in my opinion, roasted chicken, beautiful ribs, lovely salmon. Salad selections galore, hummus and chips for dipping, lots of fresh veggies.
If that won't do, you could always eat like the kids and have chichen nuggets, mac-n-cheese, and french fries and then go fill up on those wonderful little zebra domes and chocolate mousse cakes for dessert!
Try to hit the sack at a reasonable time. You will be really wiped out from travelling and those first two nights our feet really hurt at the end of the day. We come back to our room and soak them in the tub together! Note: buy epsom salts or similar foot soaking product for this trip! It will set the tone for a great trip if you get enough rest.
Enjoy yourselves!