There's probably a scale somewhere with Discord on it, but he's been shown of being capable of manipulating his size and shape, so I imagine him just a tad larger than the other characters in height mainly, but I do like to just play around with his size now and than. :')
Eh maybe, sure! But who's to say he couldn't change 'into a dragonequus' when he got there? ^-^ Heehee! And besides, look at the cute human he's visiting. She's worthy of a look at his unique draco-equine form!