I remember when Alex was diagnosed I was worried about the whole nutritional/growth portion also. What our GI said (and it has held true thus far) "If your son is meant to be 6'2" he will still get there - but he'll probably get there a little later than the rest of the boys."
Poor Alex was the smallest of his friends for the longest time, but has grown more than a half of foot in the last year - he's now taller than me at 5'9" and he's only 16 - so we are praying for that 6 foot mark (though he is officially taller than all of his older cousins at this point which makes for fun family get togethers!
He ate mashed potatoes, gravy and corn bread (made without corn kernals) almost exclusively for the first 3 months! He took it slow (which was okay by me) then started adding pasta, cheerios, rice and other bland type foods.
As soon as he was able to eat a little more, I started adding supplements: daily vitamin, B12 (for energy), omega 3s, and protein powder (going light on the protein powder as I was told it can be difficult to digest).
Today he eats just about everything except the raw veggies and other no-no list items.
Praying for you all!