Hi!
It seems like you've gotten most of your questions answered, but I just want to give you some input on the clipping-part as well, as it can't be stressed enough.. Don't let them clip your bird! I'm thinking some breeders want to clip the young birds because:
1. When clipped they can't flee and therefore seem more tame, so the customer will more likely be "satisfied" and won't return the bird. If the bird is unclipped it will require more work to get it "tame". Although it's a completely different thing, a clipped bird might seem tame but really is just unable to flee, while a non-clipped bird that is tame is most likely really tame, as it could just fly off if it wanted to... This is something I reckon could make some new owners regret their choice to get a parrot (they might've thought it would be easier than it really is), they expected the taming process to be easy while in fact, in many cases it's not. Clipping make it seem easier, but it's a kind of false tameness. Believe me, it's going to feel so much better knowing that your tame bird actually chooses to be with you (which will be the case if you don't clip it)!
2. When the bird begins their flying training they usually suck at it. Or rather, they suck at the landing part, and if you don't set up your home properly (for a bird, that is) your bird is going to try to land on a flat wall, a flat door and whatnot, or crash into objects, which will cause a lot of chaos and probably scare the new bird owner. So, wings clipped = no crashing = new owner won't be scared and feel uncomfortable = less likely they return the bird. I know it sounds weird but I do know some people who actually had this problem, they thought there was something wrong with the bird and/or just found it too uncomfortable so they simply returned it. Some tried with another species and got the same result, and some just didn't get another parrot again.
Also worth noting is, that a clipped bird may still crash and will more likely keep doing so for a longer period of time, so it really isn't very smart in that regard. What would be smart, on the other hand, would be to not clip your bird, flight train it a lot so it becomes a good flyer (and lander!) and set up many places for him/her to perch. It takes more effort but you will have a healthier parrot and the risk of him/her crashing into any precious objects (the bird getting hurt and said object ruined) will be much smaller.
There's only one answer really, to why a bird gets clipped, and that's the comfortability of us humans. A bird (unless there's some really special circumstances) never benefits from being clipped, if they did they'd be clipped naturally. Obviously, they are not.
Parrots are difficult animals to keep in good health as their needs are so different from ours (it's a lot easier for a human to figure out what a dog or cat needs as they function in more similar ways) and one of the best things you can do to prevent diseases or disorders (both physical and mental) in your bird is to let it fly. It enhances their breathing, their metabolism, their mental well being, their sociability, their confidence... Many parrots are prone to illnesses in a human environment and therefore I think it's almost our duty to do what we can to prevent as many of them from happening as possible.
I hope at least half of what I wrote is understandable, I'm currently exhausted from too much reading of boring literature, so if something doesn't add up or make sense, feel free to ask what the hell I meant
Also, to end this reply, I just wanna wish you good luck with your parrot ownership, I also briefly know a guy who breeds Alexandrines and he claims they're absolutely lovely. I don't know much about them but if you've decided it's the species for you, I hope it'll turn out great!
Best regards,
Sara, Penny & Joy