Ooooh, I was MIA when you were actively posting this thread!
Congrats on the new haul! Hope that quarantine goes well for them! I would maybe consider doing a run of melafix as a just in case as well if it was my tank. That way you cover parasite and a bit of antibiotic/antifungal
I had no problems with hatchets when I was younger, but as an adult, they are so prone to ick that it isn't even funny. They're always the first ones in a tank to sprout cysts.
Neon tetras are very hit or miss. And neon tetra disease is not something that's easy to spot. If it WAS neon tetra disease, that is caused by a parasite and angelfish are susceptible to the parasite as well. Weirdly it seems cardinal tetras are a bit hardier though? As far as I know, there's no real cure for it... ;n;
Photos of your tank really made me miss working with fish! One day I really want to start up another tank of my own, just not in the cards with rental agreements being the way they are sadly ;n;