Well...you can't give them too few treats as long as their regular feed gives them everything they need.
If you want them to lay lots of good eggs for you, you want their feed to be the majority of their diet. I can't give you a hard number on that. Also depends on what you mean by "treats".
Mine get some leftovers most days. I haven't had problems with overfeeding them, mine stop eating when they're full (leaving the dog to finish up).
So I guess it depends on what you mean when you say "treats" but I'd say you're pretty safe if you keep it to 5% of their daily intake of food.