How many treats is it OK to give and is there anything off limits.

[CochinBantams]

I give my flock blueberries (my husband manages a farm); lettuce, tomato and other cut up veggies. I give the fresh parsely and cilantro that I have in my garden and even pull grass/weeds for them. I give the bread once in awhile and when I can afford it I will give them dried "Happy Hen" worms. They are not able to go free range because of the hawks in the area which concern me. Can these type of foods be over done when given along with the laying pellets, and scratch feed?