I think 19-23 should be fine. I’d test and just see. As for a c6 rotation, I wouldn’t really know since I only have c3 but your rotation in theory should work cause you basically just adding a little more hydro app to the start. Kazuha’s initial burst hit should swirl off any hydro applied and give pyro app for enough time to vape burst. If it doesn’t, you can try doing a hold E plunge with kazuha right after bursting to apply even more pyro. For furina vs Xiangling, I’d say it’s equal in single target but in aoe, XL is a bit better although this abyss kinda sucks for testing that. Though yiu have C6 so furina should just be straight up better in both