Welcome to our newcomers! This is a great time of year for reading and learning.
Lees, I'm really happy to read that your girl seems to be okay and recovered from her experience, whew!
There are so many opinions about the right number of square feet per chicken it's hard to know how much is enough until you get too many for your space. As a general rule I try to stay with 4 sf per bird in the coop, but every flock is different - for some that will be more than enough, for others, not half enough. It partly depends on the size of your hens and their general demeanor/personalities. This is where it helps to gather input from people here who have had breeds you are interested in, because winter is cold and summer is hot, and that can impact how well the size of your coop fits your number of hens.
In a 4 x 7 coop I'd probably start with 5 or 6 and see how they do. While adding new hens to a flock can be problematic, realistically, 6 hens will usually give you 3-5 eggs per day, or 2 to 2.5 dozen a week. Unless you have a large family that has eggs for breakfast every morning, that should be plenty.
Every breed has its common characteristics, and individuals who are nothing like the norm for the breed. I have never had Black Australorps, but hear they are really reliable and generally easy keepers. If you are more concerned with egg production and economic use of food, Leghorns are probably tops but they lay white eggs and can be a bit on the skittish side - great for free ranging but maybe less great for those who like chickens they can pick up and hold, so for brown eggs and a calmer bird I'd probably listen to Wendell (wsmith) and consider Dominiques. They're pretty, good layers, use their food efficiently, and it so happens Wendell will probably have some this spring

Others that may fit that definition would be Rocks, Orpingtons, Sussex, and well bred Rhode Island Reds - the bad name they get for being testy is largely attributable to hatchery stock, I am told. There are many others of course, and the nicest backyard laying flock is probably a mixed one so you have a variety to look at and eggs that are all a bit different. Here, we enjoy the heck out of watching our Blue Cochin run for treats
Other things to consider are predators, and in neighborhoods you still have hawks, raccoons, fox, and the occasional coyote as do those of us in "the sticks" but you additionally have neighborhood dogs, which are probably the biggest threat to your flock. I recommend a roof of some sort on your runs, preferably one that will withstand the weight of a fat raccoon, and a locking latch on everything. Bolt snaps work here, but there are a multitude of options that are reasonably priced and not difficult to install.
A few of us will have eggs, chicks, and started pullets this spring, some purebreds, some hatchery stock, some crosses, all raised to the best of our abilities, and I doubt you can go wrong with any of us. Wendell will have Doms, I will be selling started pullets purchased as day olds from McMurray, Chick-In-The-Burbs will be hatching some eggs, and Coloradogal is almost year round hatching eggs in her quest to develop the ideal Colorado Landrace chicken - she has gotten some beauties

And Shyscreations has gorgeous Silkies and some other Bantams. There are doubtless others here and elsewhere on BYC. A few of us have put together orders from a couple of breeders for the spring, and I am waiting to hear from an in-state breeder who has some nice Rhode Island Reds, I'm told, as there are a couple of people here who want them, and I'll probably get a few and grow them out to see if I like them. My main focus as far as breeding will be Speckled Sussex and Light Brown Leghorns, but I am probably going to use some of the less-Speckled Sussex to work toward a Red Sussex, which is a very rare bird indeed, so I expect for a few years to have sparsely-Speckled Sussex in the Reach for a Red
If you are set up to raise day olds or hatch eggs, you can pretty much have your pick; if you prefer to purchase started birds or pullets at point of lay, and want to do so locally, it will limit you to some extent, but across the state there is a surprising number of breeds available if you look hard enough. Every stage of growth has a new price point - eggs are usually the least expensive, day olds next, then started, then point of lay. Each primarily relates to the amount of input required from the breeder/seller as well as the current value to the new owner - do you want to feed pullets for 5-7 months, 3-5 months, 1-3 months until you get eggs? Or do you want to incubate eggs for 3 weeks and then feed for 5-7 months, weed out the roosters, etc.? Roos of most breeds can be good dinner in a few months, but if they start to crow early you might not want to deal with it.
We are in the process of setting up a new website for Colorado chicken folks - those who have chickens, and those who are interested - just started the project so it may be a week or a few before we have anything of substance to show you, but the domain is reserved and the home page is started.