The issue with Whimper (the OC) is that he's described as a bullhead (long story), which means his muscles are very defined. With Big Mac, you see his strength demonstrated, but no definition on his muscles. The only stallion that has definition is comedically huge and has very small hooves, which I can't use as a reference. Big Mac, as a child, doesn't look particularly strong and it's the appearance that makes the character a bullhead. Basically, I think I just need to sculpt out something final and then make a vector out of that. Can't keep changing it.
Alpha and Omega did get the wolves walking on two legs nicely, but the arms were definitely made for four-legged motion. So there is biped-to-quad switching, but not where they'd have human-ish motions quite yet. And yeah, the transforming would be what the corrective shapes are for.
The main difference between bird wings and fairy wings is that bird wings fold against the body, whereas fairy wings do not. So... using Rigify in Blender, I'd do fairy wings with a finger sample, and alicorn wings with an arm sample. Anatomical accuracy is just simpler to get right and keep track of.
(Twilight Sparkle:) "You can't fold your wings? How do you sleep?"
(Will:) "Pretty well, thank you."
Come to think of it, wouldn't it be cool if the Fillies shared rooms? Rose and Lynn bunking together, or Will and Cedric (ship ahoy!).