Ideally you want 6-7 feet tall. Even so, ensure that you’ve clipped their wings properly.
If you toss a new hen into an established flock then yes, they’re going to attack. And there’s nothing you can do about that part because throwing new hens into an old flock means that everyone has to fight for a place in the new pecking order. Good thing is this doesn’t usually last more than a week. If you’re going to add more hens then put in all the ones you plan to introduce for the season so you don’t have to do this again and again. If you haven’t already, set the new chicken aside for a few weeks to make sure they aren’t sick. If that new one is a carrier for Marek’s, for example, and your flock hasn’t been then they’ll all be infected. Another thing is to introduce the new bird(s) at night so they wake up and don’t notice the new one as much. And if they aren’t big enough to defend themselves then they don’t need to be put in with the big ones yet.
Generally chickens will eat their own eggs if they are low on protein and/or calcium. If they are lacking something substantial in their diet like calcium or protein, boost this by providing crushed oyster shell and add more protein by moving them to a new area or purchasing bait worms if they can’t get enough in your yard.
If you have a hen that just won’t stop pecking at the eggs (which happens) then you might have to make nesting boxes that slant away and hide the eggs so the hens can’t get to them.
If you’re just starting out and/or someone dropped a bunch of hens on you, you’ll need the following: a chicken coop (we have some lovely plans for making your own, so check those out!), some type of flooring for outside, perhaps pine shavings or straw food and water and lastly L-O-V-E.