My son coming to 18 mths. During his 16 month injection, I asked the pediatrician whether can offer seafood, and pediatrician said can try in small quantity.
So far, I only tried once to give him prawn. I made dumpling (shui jiao) and added a bit of minced prawn to the minced pork. He was ok. When we go to Jap restaurant, we gave chawanmushi (not sure if any seafood used in making the stock or not). Recently he even ate a bit of my california handroll which has some prawn roe.
For chicken, I started very early like 10 mths, minced in his porridge. I only use kampung chicken.
For brown rice, I give since 8 or 9 mths, cooked in porridge. Usually mixture of white rice, millet and brown rice. Nowadays, I cook rice half white rice and half brown rice. dont't think it'll be heaty if he has sufficient water, fruits and veg.