Thanks for the comments. I definitely learned a bit from this ordeal. I'm going to store this tank for a while until the 60g build has been running successfully for a decent amount of time, maybe closs to a year. I purchased a 20g tank yesterday that I plan on setting up as a QT. I'm considering a 2nd one so I can QT both corals/inverts and fish, but the cost of another decent light might put a damper on that.Very unlucky.
Things were progressing but the tank needed some more time to mature and I think you would have been fine.
Here the newness of the tank and its residents combined with the power outage just really drastically raised the fishes stress level, making them more and more susceptible to disease.
Eventually some got there and it was like another punch to your system.
Don't beat yourself up too hard. Are you putting the 75g away for a bit until you have the cube reef up and running?