That's great! We're collecting stories about peoples' first impressions of Pony (https://www.ponylang.org/categories/my-first-pony), so if you're interested in contributing to that please get in touch.
I'm an engineer at Wallaroo Labs and I've been learning Go so that I can add a Go API to Wallaroo. Your analysis looks pretty spot-on based on my experience.
The buildmodes is go definitely make it easy to call Go from other languages. The trickiest thing I've run into so far with calling Go is that you aren't supposed to hold on to Go pointers outside of Go code, so I'm having to jump through some hoops to hold on to objects between calls.
I have an RFC for Pony that I need to finish up that will let you call Pony function from C. I'm planning on getting around to that soon, as I think it will help improve our FFI story.