Take it one meal at a time! My son (age 5, with Aspergers) has been GFCFSF (soy free) and Feingold (no artificials or preservatives) since last October. It really is a crapshoot - for every 20 recipes I try, he might like one of them. But when he DOES like it, it goes into my rotation. I have a menu set now for breakfast and lunches for every day of the week. Being an Aspie - he likes the regularity and I like that I don't have to buy much to surprise him!
Some tips -
Don't try to immediately make substitutes for his favorite things. For example - don't try to make a GFCF mac n cheese to start, there is no substitute and he'll hate it. Go as natural as possible - all fruits and veggies are a go (well, except corn). Eggs are also a great protein source, as are meats.
Message boards can be a lifesaver! There are 2 GFCF groups on Yahoo of which several members also are corn free and rice free. They can give you links like crazy.
If you get a good GFCF recipe, it can be tweaked to eliminate your other concerns. My favorite blog that is kid-friendly is Ginger Lemon Girl (gingerlemongirl.blogspot.com). She doesn't market it as "for kids" but I've tried about 15 recipes off her site and my son has loved every one. Her baking items are especially good, pancakes and muffins and waffles. These are great because they can be frozen, and they can be served for ANY meal - don't limit breakfast foods to breakfast! Eggs, pancakes and bacon can be great for dinner as well.
Rethink your idea of a "meal" - whatever you feed him doesn't have to be a casserole or 5-course dinner. I have a mix of things on hand that I pick and choose from - shredded chicken, potato chips, fruit, CF yogurt (So Delicious coconut milk yogurt), banana dogs (on cinnamon raisin bread, we use Rudis), hard boiled eggs, etc. I grab a few of each and put them on his plate. In the summer, we use muffin tins (12 tin) and I fill each one with something different. It's much easier than trying to plan an entree, and he loves the presentation.
Since your child is on the spectrum too, I would like to suggest one more diet for you (as if you need one, I know!). Look at the Feingold diet (feingold.org). It eliminated all artificial coloring, flavors and preservatives. We had as many behavioral changes with that diet alone as we did with GFCFSF - his tantrums and hyperactivity simply stopped with Feingold. You'll find a lot of GFCF things are already dye-free (like all of Ian's and Annie's Homegrown), but be wary of candy. Surf Sweet is a great company we use a lot, gummy bears and jelly beans that are naturally colored and flavored.
Feel free to email me with any questions!
S.