Pony-horse liminal space is the best size! And a really cool description for it. Our horse was on the horse-feel side of the same height, due to being half Arab (fortunately, not the freaky twitchy half), and I have been similarly spoiled in my expectations by him being really smart and great to work with, so what you're looking for makes perfect sense to me.

Also, your planning-ahead detail is, as expected, quite thorough and eminently reasonable.