The poop description sounds like what would naturally happen changing diet. And if it's coming right then your baby will be right.
I wouldn't worry about the grass. My babies eat high quality dog food (Nutro) and they still nibble on grass. They need the fibre (just like we need fibre) to keep things moving.
Small amounts of fruit should also be fine (it's fibre again) - although quite high in (natural) sugar too! (But no raw onion - I've heard it's toxic).
A few people-food treats won't harm your doglet. Variety is the spice of life
