Your Tauren isn't going to be able to get a Mechanostrider, sorry. You can only champion the races on your overall faction. In your case, you can only champion Horde races. You'll need to do Tauren first, then when you've 'finished' with the Tauren you can choose to branch out to the others. At least, that's how it worked when I was doing it on an earlier iteration of the PTR. I don't think it's changed, though.
Somewhat related to this question: There were people in the comments yesterday suggesting you couldn't champion a race until you were Exalted with them, and that's just not true. You don't need to be Exalted with anyone here. In fact, part of the purpose of this event is to help you get Exalted with them without slaving away in the runecloth mines.
"Is the same thing as the ammo bags gonna happen to the warlock soul shard bags since they are upping the base number of shards to 32, which is the biggest bag you can get right now for them. Is so, why make a pattern for the bag available only after grinding out Ebon Hand rep?"
The ammo change and the Soul Shard change are working in two entirely different ways. Soul Shards aren't stacking differently like ammo. Soul Shards still stack one at a time, but you can only carry a maximum of 32 Soul Shards at a time. This is because they changed how Drain Soul works. You have a chance to generate a Soul Shard every time Drain Soul ticks, so if they didn't put an upper limit on the number of shards you generate, your bags would fill up with them unless you had a mod deleting them all as they were created.
A raiding Warlock will probably still want to carry an Abyssal Bag around for extra room for all of the shards. The non-raiding non-PvPing warlock probably doesn't need a big bag like that, because you probably don't need 32 shards.
"I have a new question that I don't think I've seen the answer to anywhere. Does the +10% XP bonus that the Bind on Account Heirloom shoulders give apply to leveling hunter pets? I'd like to get some confirmation before dropping the emblems on them. Thanks!"
I don't think it applies to pet, but it's nearly impossible to outlevel your Hunter pet these days, they need dramatically less XP than you do to level up. If you're leveling your Hunter, yes, buy the Heirloom shoulders. They're wonderful. If you're a level 80 Hunter thinking about buying Heirloom shoulders for the purpose of leveling up new pets, no, it's not worth it.
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