[I would have positioned the 100 gal tank further out from the wall so I could service the thing far easier.
I would have had a quarantine tank set up, doubling as macroalgae tank and actually used it...
I would have had Flatworm eXit on hand and used it on all of my new fish and corals...
I would have taken the death of my second newly-bought Flame Angel as a sign from God that perhaps there were other fish in my future and quit buying those suckers...
I would have realized that when the LFS guy sez, 'I've had this fish for several weeks and..' doesn't mean that fish has bad breath or unacceptable social habits, it means that that there fish is prolly well-acclimated, disease- and drug-free and a good bet to live a while in your home tank.
I would have realized that when the LFS guy sez, " I just got this in and...' is a great non-buying opportunity for you unless you are okay with being stupid with your money. The mortality rates for newly-arrived fish is just unbelievable, something on the order of 50% or more. Flame angels...
I would have realized that, like programming, there are a zillion ways to keep a saltwater tank and there seems to be no "Best" way, other than what is working for you right now - your best way being someone else's idea of a nightmare...but if it's working, that's good enough...
I would have realized that buying a nice upscale car would have just as inexpensive as keeping saltwater tanks and maybe even cheaper.]