Your stats look weak a bit for Ultra Nghtmare. I'm not an expert, but i use Cardiel as well, with similar stats, and the best i can run is 2-key Nightmare because sooner or later, the boss gets you right when you dont have your buffs on, or he kills all your team, they revive, and he kills them again.
UNM is a rather a big jump from NM. The difference in difficulty is pretty big. I think that while you're trying to improve your gears and Main Hall and what not, trying to build a perfectly tuned team for UNM with 4* or 5* gear is pointless. You will often replace your pieces, throwing your whole team out of balance.
Stick to NM for now, and 1-key brutal and hard for extra chests if you can run all 4 keys in same day.