All the responses here have been super helpful. It's nice to get some various perspectives on this name.
I really like classic names steeped in history, but this one also seems more 'accessible' to me than a lot of the other old Latin and Greek names I've found. It's ancient but seems somewhat 'fresh' too. It feels like a strong and solid name for an adult but also like a name that would suit the newborn through youth years, especially with the NN option. It's meaningful ("to rejoice"). It's uncommon, but not totally unfamiliar feeling. My parents really like it (moreso than Kian).
And the negative things about it just don't seem like such a big deal. I think the Twilight connection will not be caught on by most people (and five years down the road, by even less people). The spelling and the pronunciation may have a few issues here and there by some people, but I don't think that's a big deal (my name and several of my good friends names growing up were mispronounced regularly and I never knew anyone who was really bothered by this).
I think it's up and just about matched Kian as a tied for top choice....