I don't have any experience with the leghorns but I have raised Black Astrolaups and Americana's for 2 years now. The blacks are very friendly (great layers) and the Americana's tend to be a lot more shy but I love their colored eggs, and their chicks are the cutest (look like little chipmunks).
I have read that to keep prediters out, you need to burry part of your fencing with it coming out like an "L" under the dirt (with the L facing OUT of the yard). This makes the preditors who dig, dig into the fencing, not under it. You will want to have a 1" chicken wire fencing on the bottom, in case you have chicks to keep them in the yard, and can put the 2" up higher (since it is cheeper, you'll want to primarily use this), you will need a covering on your yard as owls, hawks, etc like to carry off small ones. (don't know what kind of birds you have where you are at, but keep it in mind).
As for your coop size, chickens don't need a lot of room in a coop. I have a large coop and the hens seem to huddle together in one corner of the coop while there is lots of other roosting space left. And one fact that surprised me when I started, is that they all lay eggs on top of each other in a favorite nesting box. You will only need to have around 3 boxes for your eggs. Silly me thought I could assign a box for each of my hens so I could keep track of who was laying and who wasn't. (That is city girl thinking).
You will want to make your yard as big as you are able too though. If your chickens are too crowded, they will start picking at each other (they do it anyway, but it will be a lot worse, like naked hens).
Hope this helps.
Gayle