Thank you both, I suppose some professional help couldn't hurt. Frankly, given the feedback and anecdotes, I'm lucky it hasn't gotten worse already! Chah, despite his rebellions, remains a fundamentally kind animal (in my totally unqualified opinion).
It sounds silly, but when he nips, he moves his head out of the way to do it next to you, and when he bucks, it's only a few inches, once in a ride (then I scold him and that's it for that time). When he raises a leg, it's always the one opposite to the side you're on, and never, ever results in a kick or even a try (so far). So you see he's frustrated and a bit aggressive, but he's also deliberately trying not to do harm so far.
I want to correct everything of course, and certainly don't take an animal this size for granted, regardless, but let's just say we've all seen horses be much more direct and proactive in their efforts.
I work with the stable owners (lifelong horsemen/women) regularly, and strangely enough here is Switzerland, my part-time neighbor is a Cheyenne Indian horse-whisperer...
Overall I know he's a great animal, and I'm confident that with the right approach he can be corrected. Thank you again for your time and feedback