Maybe you can check how your mother in law cook the porridge? I think the consistency of porridge is impt in determining how fast baby eats their meal. My son eats faster when it's done congee style than teowchew porridge style ie porridge cooked longer under lan4lan4. As for meat and veg, go w agaration, there's no right or wrong I give mine about 8-10 stalks of baby spinach or 2-3 big broccoli florets as a serving.
Cooking wise, you can throw in the veg and fish into the slow cooker, they will be cooked until soft n mashy n should be easy to eat already so you dont have to puree.
Porridge recipes- fish and greens, sometimes add pumpkin/carrot/dried scallop to sweeten, cook till congee consistency
potato recipes - potato and greens and protein, steam n puree