Breeds to mix with what I have and other newbie ?'s

Well, I'm no expert, but I have been reading on here a lot (too much!) Let's see what I can help with. (I'm sure I'll say something you already know; just ignore it if so!)

I have about 10 breeds, mostly heavy or dual purpose, and my black Australorps are by far the friendliest. I know BO's are considered gentle and friendly. I never had red stars, but I believe they also usually are, so you probably want to stay with friendlier breeds. Most people don't have any trouble with different breeds living together. Sometimes the breeds may group themselves together and sometimes they just mingle. Problems seem more related to the personality of the individuals, or to roosters, though breeds do have personality tendencies. I have read that BO's tend to get bullied because they are so laid back. So in your situation I would stay with the friendlier or more laid back breeds. Here is a link to a "chicken selector tool" that might help: http://www.mypetchicken.com/ And Henderson's breed chart is chock full of breed info: http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html. Both also have info on cold weather breeds. Although, truth is, chickens do so much better with cold than heat. You can get frostbitten combs and toes, but it really doesn't take a lot of coop to avoid that. People in northern Alaska keep chickens....

Your BO's are a distinct breed, but your red stars are a sex link, which is already a "mutt," or cross breed. The BO's will breed true but the red stars will not. The whitish one with the green legs and muff is an EE, easter egger, which is also already a mutt, or cross breed. (If it does not already have a muff, it may not get one.) SOME of them lay blue eggs. They are usually sold by the hatcheries as Ameraucanas, but they are not full blooded Ameraucanas. You can read on here for hours about Auracanas, Ameraucanas, and Easter Eggers.

Yes, when roos breed hens of another breed, they make mutts; you will also see them called "designer chickens," a bit tongue in cheek, of course. Many on here feel this is a good thing, creates what is termed "hybrid vigor." Others try to breed a particular breed for certain "desired" characteristics and have a real problem with mixing breeds. I just ran across a really interesting thread on this subject: https://www.backyardchickens.com/forum/viewtopic.php?id=181225.

You said you have read that a few specific crosses make certain breeds. This sounds like you are talking about sex links. But a bird like a red star is not considered a breed, it is considered a hybrid, or cross, or mutt. Bottom line, if you are OK with mutts, then have mutts! That is what I am going to do.

Hens store semen for about 3 weeks, and can produce fertile eggs this long after mating. Although, of course one mating might not do the trick. Some breeds have some trouble with mating -- Cochins is one, if I remember correctly, and I'm not sure BO's don't also have trouble at times, because of their very fluffy butts.

There is a good way to tell if an egg is fertile before it starts incubating -- but you have to crack it open. There will be a "bullseye" spot on the yolk if fertile, and a whitish one if not. A search on here for bullseye will produce some good threads and photos. And yes, if you want to know if it is fertile without breaking it open, you must candle after it has been incubated for a few days. And that is about all I know about candling and incubating!

Two more things: The only stupid question is an unasked question, and, good luck!