There is a thread at the top of the WISH board called "Eating Healthy" and it lists the nutritional information for a few Disney items, but not many. I think the idea was that everyone on the WISH would get a few bits of info on every trip, and eventually we would have a good list..... but it doesn't seem to have happened.
My first suggestion would be to contact the restaurants in advance, tell them that you are on a restricted diet, and the chef will talk to you when you arrive for your dinner. I'm not sure that the chef could provide nutrition information, but at least they could make your meal without (or with) certain items that would obviously be a problem, like heavy cream, extra oil, etc.
As far as counter service.... stick with what you know! It is a whole lot easier to figure out the nutritional information for a piece of grilled chicken, than for something more complicated. Stick with plain veggies (no sauces, cheese, etc), plain salads (you could even bring your own dressing), plain meat grilled meats and fish. Don't be afraid to "make yourself" something special .....like order a grilled chicken sandwich without the bun and a small salad, top the salad with the chicken and use your own dressing. Order from the kids menu whenever possible for smaller portions or plan on sharing. My DD and I do this frequently. Since it is hard to take leftover foods with you, it makes for less waste when you share. If you weren't doing the dining plan, I would say to plan to bring in some of your own foods. But that would be a waste on the dining plan I suppose.
I'm SURE that it goes without saying to avoid french fries, hamburgers and hot dogs, and desserts!!

But be sure to have at least one treat!! A Dole Whip would probably be a good choice! Good luck.................P