I've started on my judgments but not finished them; I will not have them done before the deadline and I am, at this point, exhausted. I am going to have to post the DCC round soon and then get sleep. I promise I will finish as early as possible tomorrow.
Since I'm fairly confident the mana tags haven't started reordering symbols: Did you edit your post? If so, when?
One of the really awful things about this forum's software is that edits made too close to when the post was originally made will not only not display, but will prevent any further editing that isn't "substantial" enough as well. I would suggest editing your post again and typing, say, "placeholder" at the bottom, then removing it a few minutes later once the correct text is displaying.
It's not an oddity, it's in fitting with how every other color combination is written. One way to explain it is by imagining the mana symbols not in a straight line but as a pentagon. The shortest, least interrupted, clockwise path (I hope I'm explaining this in the right words) between two symbols is how they're ordered.
Another way to explain it is that each color has an allied color that comes before it, an enemy color that comes before it, an allied color that comes after it, and an enemy color that comes after it. Orders of shards and wedges are determined by the central color; black goes before green when they're together, and blue goes after green, so when it's all three of them green goes in the center and it's BGU. Back in Apocalypse, the "center" color was placed first for some reason but there was a templating reform in Tarkir block to put wedges in conformity with how shards are ordered.
The letter of the challenge itself doesn't actually exclude artifact creatures at all. I don't think the clarification was meant to be exclusive: the cards "can be" any of those things (including "having any other subtypes somehow" by having another card type) but there's no "can't be" that prevents the cards from being other things.
EDIT: And I'm confident that if the Lion had meant noncreature artifacts, he would have said so explicitly.
Yes, Magic (i.e. Chicago manual of style) ALWAYS uses the apostrophe-s - what Leo always calls the Saxon genitive - to form a possessive, even after a double s. See Enchantress's Presence. This is an objective issue.