Everyone is here to help and there are a lot of good refers in the area which have certainly helped me so much in the past and will hopefully help me when I get past my understanding on this new tank.
I'd drain your tank just down below the Bryopsis and spray them with the peroxide, and let it sit for a few minutes, then refill with some clean water. That and turning your lights down should knock it out for you and keep everything on track for you. Repeat if you missed something. The WC will certainly be good for the tank as well. Biopsies is a PITA when you have it, so best to get it now and try your best not to reintroduce.
Here is for for thought for you. Looks like you have Marco rock or some other dry rock. This came from some geological event that wiped out that old reef. Everything died. Then is was buried underground for a however long and whatever eventually covered it was not a nice clean pristine reef. It would be safe to assume all the pores in that rock are chock full of stuff you would prefer is NOT in there, so it needs time to leach out, re-populate and just get healthy again. That takes time and water changes to dilute/export it. Just focus on getting past that. You can 100% water change you way out everything right now and use the cheapest salt available as you don't need to worry about all the levels and chemistry. It will get there then you can tackle the complexities of keeping acros happy and that chemistry lesson. You can spend the next few months digging into that and sorting through the facts and fiction. Maybe post what you plan to do and get some solid opinions from the smart people here, then choose the next corse of action after consideration.
Figure out how you want to get live sand?